Efficient isolation of backup versions of data objects affected by malicious software

A system for efficient isolation of backup versions of data objects affected by malicious software includes one or more processors and a memory coupled to the processors. The memory comprises program instructions executable by the processors to implement a backup manager configured to receive an indication that a data object is infected by malicious software. In response to the indication, the backup manager is configured to identify a particular backup version of the data object to be excluded from a data set to be used for a restore operation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to computer systems and, more particularly, to secure backup and restore techniques used in computer systems.

2. Description of the Related Art

Security of information technology (IT) assets is an ever-growing concern in today's enterprises. As more and more of enterprise computing resources are linked directly and/or indirectly to external networks such as the Internet, the likelihood of various types of network intrusions and infections by malicious software such as viruses, Trojan horses, worms, etc. is only expected to increase. Although a number of different techniques to enhance the security of enterprise computing environments have been implemented over the years, such as various types of hardware and software firewalls, virus detection tools, and the like, malicious-software attacks continue to succeed at least temporarily from time to time, often resulting in large productivity losses and/or data loss. For example, even though virus detection tools are frequently updated to recognize the latest viruses that have been identified, new, as-yet-undetected viruses are just as quickly being transmitted around the Internet by unsuspecting e-mail users, file sharers and other users. By the time a solution for a particular virus is developed and widely deployed, it is often the case that the virus has already infected hundreds or even thousands of systems around the world.

In some scenarios, for example where the computer systems at a particular enterprise are regularly backed up, an infected version of a particular file or other data object may be inadvertently backed up. At the time the backup version of the file is created, for example during a daily scheduled backup, the existence of the virus may not have been detected. The fact that the file is infected may not be detected even if a full virus scan of the data set being backed up is performed, since the virus detection tool used may not have been updated to recognize the virus.

For reasons such as those described above, it is often possible that by the time a live or online version of a particular file is found to be infected by malicious software, an infected backup version of the file may already have been created. The live version of the file may be quarantined and/or deleted when it is found to be infected, which may require a restoration of the file from a backup version. However, if the restore operation happens to use an infected backup version, the malicious-software infection may be reintroduced into the live data of the IT environment.

SUMMARY

Various embodiments of systems and methods for efficient isolation of backup versions of data objects affected by malicious software are disclosed. According to one embodiment, a system includes one or more processors and a memory coupled to the processors. The memory comprises program instructions executable by the processors to implement a backup manager configured to receive an indication that a data object (e.g., a “live” or “online” data object that is accessible to users and applications without requiring interaction with the backup manager) is infected by malicious software. In response to the indication, the backup manager is configured to identify a particular backup version of the data object to be excluded from a data set to be used for a restore operation. For example, in one embodiment where multiple backup versions of a given data object may have been created over time, the backup manager may be configured to perform an analysis to determine whether any of the backup versions are also infected, or are highly likely to be infected (e.g., if a backup version was created after the data object was last modified, the backup version may be inferred to be infected). If a backup version is found to be suspect (i.e., if it is determined that the backup version is infected or has a high probability of being infected), in one embodiment the backup manager may be configured to generate metadata (e.g., metadata stored in a backup catalog) indicating that the backup version is not to be used for restores.

In some embodiments, in response to the indication that a data object is infected by malicious software, the backup manager may be configured to determine whether a backup version differs from the infected data object using an efficient difference analysis, without for example actually scanning the backup version for malicious software, and to use the results of the analysis to determine whether to prevent restores from the backup version. For example, the backup manager may be configured to compare values of one or more attributes (such as last modification times, file sizes, etc.,) of the infected object with the values of corresponding attributes of the backup version; if the attribute values are identical, the backup manager may infer that the backup version is highly likely to be infected by the same malicious software and may exclude the backup version from restores. In other embodiments, the difference analysis may include a comparison of respective checksums and/or signatures generated from the backup version and the infected data object, and if the checksums or signatures for a backup version and the infected data object are identical, the backup version may be excluded from restore data sets.

A number of different techniques may be used to provide the indication to the backup manager that a data object is infected by malicious software in different embodiments. For example, in one embodiment, the indication may be sent by a malicious-software detector directly to the backup manager, e.g., using a notification application programming interface (API) supported by the backup manager, when the infection is detected. In another embodiment, the backup manager may be configured to directly or indirectly query a malicious-software detector to identify infected objects, e.g., by inspecting a list of infected data objects that have been quarantined by the malicious-software detector, or by using an API supported by the malicious-software detector. In some embodiments, the indication that a data object is infected may include return values or error codes received by the backup manager in response to I/O requests. In one such embodiment, for example, in response to receiving a generic error code (e.g., an error code that does not specifically indicate that a malicious software infection has been detected) in response to an I/O request, the backup manager may be configured to perform additional operations to determine additional information such as a specific source or cause of the error, and a result of the additional operations may indicate that the data object and one or more backup versions of the data object are infected. In another embodiment, specific error codes that indicate infection by malicious software may be returned. The return values and/or error codes may be provided to the backup manager in response to read requests and/or write requests or in various embodiments. For example, in one embodiment an error code may be returned when the backup manager attempts to read an infected data object to create a backup version, and in another embodiment, an error code may be returned when the backup manager attempts to write a copy of an existing backup version of a data object into a live data set during a restore.

In some embodiments, during restore operations for data objects that have been infected by malicious software, the backup manager may be configured to automatically search for uninfected backup versions from which the data objects should be restored. Users may be notified when a suspect or infected backup version of a data object is encountered during a restore operation in one embodiment, and permission to search for and restore from an uninfected version may be requested from the users.

DETAILED DESCRIPTION

FIG. 1is a block diagram illustrating a system100according to one embodiment. As shown, system100includes a backup manager120, a live data set105and a plurality of backup data sets125(e.g., backup data sets125A-125K). Backup manager120may be responsible for generating backup versions of data objects (such as objects110A-110P, collectively referred to herein as data objects110) of the live data set105using any of a variety of backup techniques. In addition, backup manager120may also be configured for restoring backed up versions of data objects (such as backup versions130A-1-130A-N,130K-1-130K-M, collectively referred to herein as backup versions130) to the live data set105as needed, using any of a variety of restoration techniques. The terms “live data set” and “online data set”, as used herein, refer to a collection of data objects110that are directly accessible to users and applications for read and modify operations, e.g., without requiring interactions with the backup manager120. In contrast to live or online data, backup data sets125comprise versions of data objects that may generally require restoration by the backup manager120before they can be read or written by users or applications—thus, backup manager120generally serves as an intermediary for access to backup versions130. Data objects110may comprise any of a variety of different virtual and/or physical storage objects in various embodiments, such as files, directories, logical volumes, objects of an object-based storage device (OBSD), database management system (DBMS) objects such as records, tables, indexes, etc.

At a given point in time, one or more data objects110of the live data set105may include updates that have not been yet been backed up. Each backup data set125may include respective versions of one or more objects of the live data set105, e.g., corresponding to the current state of the live data set105at the time the backup data set was created by backup manager120. Not all backup data sets125may include backup versions130corresponding to each of the data objects110currently present in live data set105. In addition, backup versions130in different backup sets may correspond to the same data object110: e.g., if a particular data object110A is updated on a Monday and then on a Tuesday of a particular week, and backups of the live data set are created every night, one backup version130A-1of the data object110A may be created and stored in a backup data set125A on Monday night, and another backup version130B-1(not shown inFIG. 1) may be created and stored in a backup data set125B (also not shown inFIG. 1) created on Tuesday night.

In response to a restore operation requested for one or more data objects110, e.g., in the event that the live versions of the data objects are lost, damaged or corrupted, backup manager120may be configured to identify a set of backup versions130from which the data objects are to be restored, and restore the data objects using the identified set of backup versions. The set of backup versions130from which the data objects are restored may be referred to herein, as a “restore data set” or a “data set used for the restore operation”. It is noted that the set of backup versions130included in a restore data set may not all have been created by the backup manager in a single backup operation, and that backup versions from two or more different backup data sets125may be used for a single restore operation. The backup manager120may maintain configuration information (e.g., information indicating which backup versions130correspond to a given data object110, etc.) in a backup catalog or backup database in some embodiments.

The backup manager120may be configured to receive indications that one or more data objects110have been infected by malicious software, such as a virus, Trojan horse, worm, spyware, adware, etc., from a variety of sources in different embodiments.

The term “malicious software”, as used herein, refers generally to any software that is intended to damage or disrupt the ability of a computer system to perform functions desired by the owners or managers of the computer system, software that is intended to utilize resources of the computer system in a manner that is not desired by the owners or managers, and/or software intended to obtain information from the computer system without the consent of the owners or managers. In the depicted embodiment, a malicious-software detector150may be configured to detect whether one or more data objects110in the live data set105are infected by malicious software, and provide an indication to anyone who reads the data objects—including the backup manager120—if an infection is detected. In response to receiving the indication, the backup manager120may be configured to determine whether one or more backup versions130of the infected data object110are to be excluded from data sets to be used for restore operations. In some embodiments, the backup manager120may be configured to perform analysis on selected backup versions130to determine which, if any, of the backup versions130are to be excluded from restores, as described below in further detail.

FIG. 1illustrates an exemplary scenario in which malicious-software detector150has identified data object110B as being infected, as indicated by the arrow labeled “1” and the large “X” indicating an infection. The malicious-software detection tool150may be configured to perform any combination of a variety of actions in response to detecting the infection in various embodiments, such as repairing, “quarantining” and/or deleting the infected data object110B, notifying a user or administrator of the detection of the infection, etc. In addition, in the depicted embodiment, the malicious-software detector150may be configured to send an indication to the backup manager120, as indicated by the arrow labeled “2”, that the data object110B is infected. In some embodiments, the indication may be sent in the form of a message by the malicious-software detection tool150to the backup manager120, e.g. using a vendor-neutral notification application programming interface or API supported by the backup manager120, identifying the infected object110B as soon as the infection is detected. In other embodiments, the indication may be received by the backup manager via other methods: for example, the backup manager120may be configured to periodically examine a list of quarantined data objects generated by malicious-software detector150, send queries to malicious-software detector150, or examine a database maintained by malicious-software detector150. In one embodiment, an indication of infection of a data object may be provided to backup manager120via a return value of an I/O operation requested by the backup manager120when and if backup manager120accesses a potentially infected backup version130, as described below in further detail. In response to the indication, in the exemplary scenario ofFIG. 1, the backup manager120may be configured to exclude backup version130K-1from a restore data set. As indicated by the arrow labeled “3”, the backup manager120may be configured to generate metadata180indicating, for example, that the backup version130K-1is a “suspect” or “infected” version of the data object110B, and should therefore not be used for restores. In some embodiments, the metadata180may be stored in a backup catalog maintained by the backup manager to manage backup data sets125.

Backup manager120may thus be able to efficiently identify those specific backup versions130that, if used for restore operations, may result in malicious-software infections being reintroduced into the live data set105, and thus prevent such potentially damaging restore operations. Furthermore, the security of restore operations may be enhanced using the techniques described above without requiring malicious-software scans specifically for backup operations, e.g., without scanning the set of data objects110that are to be included in a backup data set125or the backup versions130after they have been generated. In addition, the operations of the backup manager120may be performed in some embodiments in a vendor-neutral manner with respect to the malicious-software detector150; that is, any malicious-software detection tool or mechanism may be employed, without requiring an IT administrator to purchase or license a specific malicious-software detection tool150. Since many IT environments often have pre-deployed malicious-software detection tools, a technique such as the one described above that avoids tight coupling of backup manager120to a specific vendor or supplier of malicious-software detection technology may help to reduce overall product licensing costs.

FIG. 2is a flow diagram illustrating aspects of the operation of backup manager120, according to one embodiment. The backup manager may be configured to generate and store one or more backup versions130of one or more data objects110(block205) using any desired backup technique. The backup versions130may be generated and stored, for example, according to a backup schedule set up by a user or administrator, in which full and/or incremental backups of a portion or all of live data set105are created at specified time intervals. Not all the data blocks present in a given data object110may be copied to create a given backup version130in some embodiment: e.g., to perform an incremental backup, in one embodiment only the portions of the data object that have changed since a previous backup may actually be copied, along with enough information to allow the full restoration of the data object110from the incremental backup version and one or more other backup versions. The backup versions130may in some embodiments be stored in different storage devices than those used for the live data set105, e.g., in a different physical location or on removable media, for disaster recovery purposes.

The backup manager may receive an indication that a data object110for which backup versions may have been created earlier is infected by malicious software (block210). In some embodiments, the indication may be sent by a malicious-software detection tool150as soon as the infection is discovered. In other embodiments, there may be a delay between the detection of the infection and the indication being provided to the backup manager120: for example, the backup manager120may be, configured to periodically inspect a list of infected objects (e.g., objects quarantined by a virus detector tool) to identify data objects110that have been infected, or the indication may be provided to the backup manager120in a return value from a read or write request from the backup manager120during a backup or restore operation.

In response to the indication, the backup manager120may be configured to identify one or more backup versions130of the infected data object110(block215). For example, in response to an indication that a particular data object110B has been infected, configuration information maintained by the backup manager120may allow it to generate a list of all the previously backed up versions130(e.g., including backup version130K-1inFIG. 1) of that data object110B within various backup data sets125from which restores are still permitted. The set of backup versions130of the infected data object110may then be arranged or sorted in some order, e.g., in reverse chronological order based on the times at which they were created, in some embodiments for analysis. In other embodiments, the backup versions may be analyzed in the order in which they are found by the backup manager120, without an additional sorting step. During a given iteration of the analysis, the backup manager120may select the next backup version130to be examined (block220), and determine whether that backup version is suitable for restoration or not (block225). A number of different techniques may be used to determine whether the backup version is suitable for restoration in various embodiments, as described below in further detail. In one embodiment, for example, one or more attributes of the backup version130(such as last modification time and/or object size) may be compared to corresponding attributes of the infected data object110to make a determination whether the backup version differs from the infected version, and the backup version may be excluded from restore operations if the attributes are identical.

If the backup version130being analyzed is found to be unsuitable for restores, the backup manager may mark it as such, e.g., by generating metadata180that indicates that the backup version is suspect or infected and is not to be restored (block230) and storing the metadata in a backup database or backup catalog. The backup manager120may be configured to implement a “backup quarantine” technique to mark the suspect or infected backup versions in some embodiments, analogous to the quarantine techniques used by malicious-software detectors such as virus scanners. In some embodiments, the suspect or infected backup version (i.e., the backup version found unsuitable for restores) may be logically and/or physically removed from the corresponding backup data set125, or moved to a special location designated for quarantined backup versions. If more backup versions of the infected data object remain to be analyzed (as detected in block235), the operations corresponding to blocks220,225and230may be repeated until all backup versions that could potentially have been used for restoration have been analyzed and the analysis is complete (block240).

It is noted that in some embodiments, the operations of the backup manager120in response to the indication of an infection may vary in some respects from those illustrated inFIG. 2, or may be performed in a different order than the order shown. In one embodiment where the analysis is performed in reverse chronological order, for example, as soon as a particular backup version130is found to differ from an infected data object (or from an infected backup version), further analysis of earlier versions may be abandoned. For example, in a scenario where three backup versions130X,130Y and130Z of a data object110that has been found to be infected were created at respective times T, (T+a), and (T+a+b), the backup manager120may be configured to analyze130Z before130Y, and130Y before130X. If the analysis of backup version130Z indicates that backup version130Z differs from an infected version, analysis of backup versions130Y and130X (which were created earlier) may not be required, based on an inference by the backup manager120that versions130Y and130X must also differ from the infected version. In another embodiment, backup manager120may be configured to use multiple threads of execution to perform the analysis, so that one or more backup versions130may be analyzed concurrently instead of being analyzed one by one. In one implementation, instead of immediately analyzing the backup versions130, backup manager120may be configured to mark all the backup versions130of an infected data object110as being “suspect”, and the analysis may be performed asynchronously with respect to the indication that the data object110is infected. For example, in one implementation all backup versions of an infected data object110may be placed on a “to-be-analyzed” queue when the backup manager120receives the indication of the infection, and the backup manager120may be configured to examine, as a background task when no high-priority backups or restores are in progress, which if any of the backup versions on the “to-be-analyzed” queue are to be excluded from restores. As described below in further detail, in some embodiments “just-in-time” analysis of backup versions may be performed—e.g., the fact that a particular backup version of a data object is infected may be determined during restore operations, and if such an infection is found, the particular backup version (and/or any other infected backup versions of the data object) may be excluded from the restore.

FIG. 3is a flow diagram illustrating aspects of the operation of a backup manager120during analysis to determine whether a particular backup version130of an infected data object110should be excluded from restore data sets, according to one embodiment. The results of operations such as those illustrated inFIG. 3may be used in operations corresponding to block225and230ofFIG. 2. In the embodiment ofFIG. 3, the backup manager120may be configured to compare the backup version130with the infected data object110using one or more difference criteria, and use the results of the comparison to infer whether the backup version is either actually infected, or at least highly likely to be infected. The analysis may begin by the backup manager examining one or more attributes of the backup version130as well as the infected data object110(block305) to determine whether corresponding attribute values are identical. Exemplary attributes that may be examined in an embodiment where each data object110represents a file may include, for example, file size in bytes, last modification time, an identification of the last user to modify the file, ownership information, read/write permissions, etc. Similar attributes may be examined for other types of data objects110, such as object size, object modification time, etc., in object-based storage devices (OBSD), database record sizes and modification times in databases, and so on. If the attribute values for the backup version130and the infected data object are found to be identical (as detected in block310), the backup manager120may infer that the probability that the backup version130is also infected by the same malicious software is high. Conversely, if the attribute values differ, the backup manager120may infer that the probability that the backup version is infected is low. If the attribute values differ, the backup manager may, e.g., depending on the differences found in the attributes, either allow the backup version130to be used for restore operations (block325), or in some embodiments may mark the backup version130as potentially requiring further analysis. For example, if the size or last modification time of the backup version130differs from that of the infected data object110, the backup manager120may determine that the backup version is not infected and safe to use for restore in some embodiments; however, if the backup version130differs from the infected data object110only in other attributes (such as ownership or access permissions), further analysis may be performed.

In the depicted embodiment, if the attribute values are identical, the backup manager120may be configurable to perform an additional check, based on the actual contents of the data object110and the backup version130, to determine whether the backup version should be excluded from restore operations. If such content-based checking is to be performed (as determined in block315), the backup manager may be configured to compare a signature (e.g., a result of a mathematical function on the bytes of the object) of the data object110with the signature of the backup version130. If the signature is identical (as determined in block320ofFIG. 3), the backup version130may be inferred to have a very high probability of being infected (block330) and may therefore be excluded from restore data sets. Similarly, if the attribute values are identical and the backup manager is not configured to perform additional content-based analysis (as also determined in block315), the backup version130may be excluded from restore operations. Any of a variety of different signature generation schemes, such as various types of checksums or the MD5 algorithm, may be employed in different embodiments. In some embodiments, the backup manager120may be configured to generate the signatures for the backup versions130and/or the data objects110on demand, i.e., when needed for the analysis illustrated inFIG. 3; in other embodiments, the backup manager120may be configured to generate and store signatures in advance for at least some backup versions130in preparation for possible difference analysis. In some embodiments, content-based techniques such as checksums/signatures may be used without using attribute-based techniques.

By using attribute-based analysis and/or signature-based analysis as described above, in some embodiments the amount of processing required to determine whether the backup version should or should not be used for restore may be reduced, e.g., compared to the analysis and processing that may be required to scan the backup version. In some embodiments, the backup manager120may allow users to specify which specific techniques should be used to analyze the backup versions130—e.g., an administrator may use a configuration parameter to indicate a particular signature/checksum algorithm is to be used. In one embodiment, different analysis algorithms may be specified for different subsets of the live data set105—e.g., an administrator may specify that for any infected files in a directory D1, a checksum-based analysis is required, while for files in a directory D2, an attribute-based analysis is sufficient. In one implementation, the analysis of a backup version130may be performed by invoking a malicious-software detector150; e.g., instead of or in addition to relying on attribute analysis or signature analysis, an actual scan of the backup version130of the infected data object110may be performed.

In some embodiments, in response to a restore request, the backup manager120may be configured to identify a suitable uninfected backup version130for a particular data object to be restored.FIG. 4is a flow diagram illustrating aspects of the operation of a backup manager120during a restore operation in one such embodiment. The backup manager may receive a restore request (block405) and identify a set of backup versions corresponding to the data objects110to be restored (block410). For example, the restore request may indicate that all the files in a particular directory or file system are to be restored using the latest available backup versions, and the backup manager may assemble a list of the latest backup versions130corresponding to the specified directory or file system. The backup manager120may then be configured to restore each of the data objects110for which an uninfected backup version is available. To perform the restoration, the backup manager120may be configured to examine each of the identified backup versions to determine whether it is suitable for restoration. In some embodiments, the backup manager120may have previously marked one or more of the backup versions130as being unsuitable for restoration, while in other embodiments the determination of whether a given backup version130should or should not be restored may be made after the restore request is received.

As shown in block415, during iterative analysis of the set of backup versions130from which restoration may potentially be performed, the backup manager120may examine the next backup version. If the backup version130is found to be unsuitable for restoration (as detected in block420), e.g., if it was previously marked as being suspect or infected, or if a return value for an I/O operation on the backup version indicates that it corresponds to an infected data object110, the backup manager120may be configured to search for an uninfected backup version130for the corresponding data object110. If an uninfected backup version is found (e.g., in a different backup data set125than the one that contained the suspect or infected backup version), as detected in block425, the backup manager120may be configured to restore the data object from the uninfected backup version (block430). In some embodiments, the backup manager120may optionally inform the requester (e.g., the user or application that requested the restore) that an infected backup version was excluded from the restore and a different backup version, which may have been backed up at an earlier point in time than the infected backup version, was used for the restore.

In one embodiment, if the backup manager120finds that the backup version130being examined is infected or suspect, the backup manager120may be configured to obtain explicit permission from the requester before restoring a different backup version: e.g., a requesting user may be prompted for permission using a message such as “Backup version of file C:\xyz\a.txt dated Jan. 5, 2006 is suspected to be infected by a virus. If restore from a backup version dated Jan. 4, 2006 is acceptable, please click on the “Use latest uninfected version” button.” In some embodiments, the backup manager120may be configured to provide a configuration parameter (set, e.g., using a graphical interface, a parameter file, an environment variable or a command line option) allowing users to indicate that the backup manager is permitted to restore from the latest available uninfected backup version without asking for explicit permission when an infected or suspect backup version is found.

If no “clean” backup version130(i.e., a version that is not infected and not suspected of being infected) is available for a given data object110(as also detected in block425), the backup manager120may be configured to notify the requesting user or application that no restorable backup version is available (block435). If the backup version being examined is found to be suitable for restore in operations corresponding to block420, the corresponding data object110may be restored from the backup version (block450). If additional backup versions of the identified set of backup versions remain (as detected in block440), the operations corresponding to blocks415,420,425,430,435and/or450may be repeated until the entire set of backup versions corresponding to the restore request have been examined and the restore operation is completed (block445).

In some embodiments, the indication that a given data object110or one of its backup versions130is infected may be provided to the backup manager in the form of return values or error codes when the backup manager attempts I/O operations associated with the data object.FIG. 5ais a flow diagram illustrating aspects of the operation of a backup manager120in an embodiment where error codes from read operations may indicate infection by malicious software, andFIG. 5bis a flow diagram illustrating aspects of the operation of a backup manager120in an embodiment in which error codes from write operations may indicate infection by malicious software. As shown in block505ofFIG. 5a, the backup manager120may be configured to issue a read request (e.g., a read system call) on a particular data object110, e.g., as part of a requested backup. If the read request succeeds without an error (i.e., if no error code is returned, as detected in block510), the status of backup versions of the data object110is unaffected (block535). If the read request results in an error indication (as also detected in block510), however, the backup manager120may be configured to perform additional operations that may affect the status of backup versions of the data object110. In some embodiments, specific error messages that clearly indicate that the data object is infected may be provided: e.g., an error code such as “VIRUS_INFECTION_READ_ERROR” may immediately indicate to the backup manager that the data object110is infected. If the error code specifies that the data object110is infected (as detected in block515), the backup manager may be configured to exclude any suspect or infected backup versions130of the data object110from restores (block530): e.g., in some embodiments the backup manager may use the difference analysis techniques described earlier in conjunction withFIG. 3to identify suspect or infected backup versions. In some embodiments, however, a more generic error code (e.g., “ACCESS_DENIED” or simply “READ_ERROR”) may be returned, which does not specifically indicate that the data object is infected by malicious-software. If a generic error code is received (as also detected in block515), the backup manager120may be configured to perform one or more additional operations (block520) to determine to determine whether malicious-software infection caused the error, or more generally to identify the cause or source of the error. If a result of the additional operations indicates that the data object is indeed infected (as determined in block525), the backup manager120may also exclude suspect/infected backup versions of the data object from restores (block530). If the additional operations do not indicate that the data object110is infected, the status of backup versions of the data object may be left unchanged (block535). A variety of different additional operations corresponding to block520may be performed by the backup manager120in various embodiments when a generic error message is received: for example, the backup manager120may inspect a set of data objects110known to have been quarantined in one embodiment, or the backup manager may query a malicious-software detector150using an API supported by the malicious-software detector to determine whether the data object110on which the read is requested is infected.

FIG. 5billustrates analogous operations to those illustrated inFIG. 5afor an embodiment in which the return values indicating possible infection are received in response to write requests. The backup manager120may issue a write request, e.g., when it attempts to copy a backup version130of a data object110into the online data set105for restore (block550ofFIG. 5b). If the write succeeds, the status of backup versions of the data object110may be unaffected by the write (block580). If the write request results in an error code (as detected in block555), however, the backup manager120may be configured to determine whether one or more backup versions130of the data object (including the one being copied) are infected or suspect. As in the case of read operations ofFIG. 5a, an error code for the write may be either specific (e.g., a “VIRUS_INFECTION_WRITE_ERROR” error code may be returned to the backup manager, clearly indicating that the data object110is infected) or generic (e.g., “ACCESS_DENIED” or “WRITE_ERROR”). If a specific error code indicating malicious-software infection is received (as detected in block560), one or more backup versions130, including the backup version being copied, may be excluded from restores (block575). If the error code is generic or unrecognized by the backup manager (as also detected in block560), additional operations similar to those described above with respect to block520ofFIG. 5amay be performed to determine whether the backup version130being copied is infected or not (block565ofFIG. 5b). If a result of the operations indicates that the backup version is infected (as detected in block570), the infected backup version130(and any other backup versions that are also found to be infected, e.g., using difference analysis as described earlier) may be excluded from the restore. In some embodiments, as described earlier, the backup manager may be configured to search for uninfected backup versions of the data object110and perform the restore using an uninfected version if one is found. If the additional analysis indicates that the backup version130is not infected, the status of the backup version (and any other backup versions) may not be affected by the write operation (block580). In some embodiments, a malicious-software detector150may be integrated with, or may be configured to cooperate with, an I/O subsystem (e.g., with a file system, a volume manager and/or an operating system) in order to provide the return codes for reads and/or writes as described above. In one embodiment, error codes indicating possible infection by malicious software may be returned for both read and write operations.

FIG. 6is a block diagram of a computer host601, according to one embodiment. As shown, host601may include one or more processors605, such as processors605A and605B. In various embodiments, processors605may be implemented using any desired architecture or chip set, such as the SPARC™ architecture from Sun Microsystems or the x86-compatible architectures from Intel Corporation, Advanced Micro Devices, etc. Backup software615comprising program instructions that may be executable to implement the functionality of the backup manager120described above may be partly or fully resident within a memory610at a given point in time, and may also be stored on a storage device640. Memory610may be implemented using any appropriate medium such as any of various types of RAM (e.g., DRAM, SDRAM, RDRAM, SRAM, etc.). In addition to processors605and memory610, host601may also include one or more I/O interfaces612, such as I/O interface612A to a display device650, and I/O interface612B providing access to storage devices640, one or more network interface cards (NICs)625providing access to a network, and the like. Any of a variety of storage devices640may be used to store the instructions as well as data for backup software615in different embodiments, including any desired type of persistent and/or volatile storage devices, such as individual disks, disk arrays, tape devices, optical devices such as CD-ROMs, CD-RW drives, DVD-ROMs, DVD-RW drives, flash memory devices, various types of RAM and the like. One or more storage devices640may be directly coupled to host601in some embodiments (e.g., using the Small Computer Systems Interface (SCSI) protocol), or may be accessible over any desired storage interconnect such as iSCSI (internet SCSI), a fiber channel fabric or storage area network (SAN) in other embodiments. A storage device640may include holographic media in some embodiments. Part or all of live data set105and/or backup data sets125may be stored on any desired type of storage device640.

In addition to backup software615, memory610and/or storage devices640may also store operating systems software and/or software for various applications, including malicious-software detector150, in various embodiments. In some embodiments, backup software615may be included within an operating system, a storage management software product or another software package, while in other embodiments, backup software615may be packaged as a standalone product. In one embodiment, backup software615and malicious-software detector150may be combined into a single software package or product. In some embodiments, the component modules of backup software615may be distributed across multiple hosts601, or may be replicated at a plurality of hosts. In one embodiment, part or all of the functionality of a backup manager120may be implemented via one or more hardware devices (e.g., via one or more Field Programmable Gate Array (FPGA) devices) or in firmware.