WHAT IS RANSOMWARE? 

Ransomware is a type of malicious software cyber

actors use to deny access to systems or data. The

malicious cyber actor holds systems or data

hostage until the ransom is paid. After the initial

infection, the ransomware attempts to spread to

shared storage drives and other accessible 

systems. If the demands are not met, the system 

or encrypted data remains unavailable, or data

may be deleted.

HOW DO I PROTECT MY NETWORKS? 

A commitment to cyber hygiene and best practices

is critical to protecting your networks. Here are 

some questions you may want to ask of your 

organization to help prevent ransomware attacks: 

1. Backups: Do we backup all critical information?

Are the backups stored offline? Have we tested

our ability to revert to backups during an incident?

2. Risk Analysis: Have we conducted a 

cybersecurity risk analysis of the organization? 

3. Staff Training: Have we trained staff on

cybersecurity best practices?

4. Vulnerability Patching: Have we implemented

appropriate patching of known system 

vulnerabilities?

5. Application Whitelisting: Do we allow only

approved programs to run on our networks?

6. Incident Response: Do we have an incident

response plan and have we exercised it? 

7. Business Continuity: Are we able to sustain

business operations without access to certain

systems? For how long? Have we tested this?

8. Penetration Testing: Have we attempted to hack

into our own systems to test the security of our

systems and our ability to defend against

attacks?

HOW DO I RESPOND TO RANSOMWARE? 

Implement your security incident response and 

business continuity plan. It may take time for 

your organization’s IT professionals to isolate and 

remove the ransomware threat to your systems 

and restore data and normal operations. In the 

meantime, you should take steps to maintain your 

organization’s essential functions according to your 

business continuity plan. Organizations should 

maintain and regularly test backup plans, disaster 

recovery plans, and business continuity 

procedures.

Contact law enforcement immediately. We 

encourage you to contact a local FBI1 or USSS2

field office immediately to report a ransomware 

event and request assistance.

There are serious risks to consider before 

paying the ransom. We do not encourage paying 

a ransom. We understand that when businesses 

are faced with an inability to function, executives 

will evaluate all options to protect their 

shareholders, employees, and customers. As you 

contemplate this choice, consider the following 

risks: 

• Paying a ransom does not guarantee an 

organization will regain access to their data; in 

fact, some individuals or organizations were 

never provided with decryption keys after having 

paid a ransom. 

• Some victims who paid the demand have 

reported being targeted again by cyber actors.

• After paying the originally demanded ransom, 

some victims have been asked to pay more to get 

the promised decryption key.

• Paying could inadvertently encourage this 

criminal business model.

1 https://www.fbi.gov/contact-us/field/listing_by_state 2 http://www.secretservice.gov/contact/ 

Protecting Your Networks from Ransomware

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Protecting Your 

Networks from 

Ransomware

Ransomware is the fastest growing malware threat, targeting users 

of all types—from the home user to the corporate network. On 

average, more than 4,000 ransomware attacks have occurred daily 

since January 1, 2016. This is a 300-percent increase over the 

approximately 1,000 attacks per day seen in 2015. There are very 

effective prevention and response actions that can significantly 

mitigate the risk posed to your organization.

Ransomware targets home users, businesses, and 

government networks and can lead to temporary or 

permanent loss of sensitive or proprietary information, 

disruption to regular operations, financial losses incurred to 

restore systems and files, and potential harm to an 

organization’s reputation. 

Ransomware may direct a user to click on a link to pay a 

ransom; however, the link may be malicious and could lead to 

additional malware infections. Some ransomware variants 

display intimidating messages, such as: 

“Your computer was used to visit websites with 

illegal content. To unlock your computer, you must 

pay a $100 fine.” 

“You only have 96 hours to submit the payment. If 

you do not send money within provided time, all 

your files will be permanently encrypted and no one 

will be able to recover them.” 

What is 

Ransomware? • • •

Ransomware is a form of 

malware that targets your 

critical data and systems for 

the purpose of extortion. 

Ransomware is frequently 

delivered through 

spearphishing emails. After 

the user has been locked 

out of the data or system, 

the cyber actor demands a 

ransom payment. After 

receiving payment, the 

cyber actor will purportedly 

provide an avenue to the 

victim to regain access to 

the system or data. Recent 

iterations target enterprise 

end users, making 

awareness and training a 

critical preventive measure.
Protecting Your Networks from Ransomware

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Protecting Your Networks

Educate Your Personnel

Attackers often enter the organization by tricking a user to disclose a password or click on a 

virus-laden email attachment.

Remind employees to never click unsolicited links or open unsolicited attachments in emails. 

To improve workforce awareness, the internal security team may test the training of an 

organization’s workforce with simulated phishing emails1. 

Proactive Prevention is the Best Defense

Prevention is the most effective defense against ransomware and it is critical to take 

precautions for protection. Infections can be devastating to an individual or organization, and 

recovery may be a difficult process requiring the services of a reputable data recovery 

specialist.

The U.S. Government (USG) recommends that users and administrators take the following 

preventive measures to protect their computer networks from falling victim to a ransomware 

infection:

Preventive Measures 

• Implement an awareness and training program. Because end users are targets, 

employees and individuals should be aware of the threat of ransomware and how it is 

delivered. 

• Enable strong spam filters to prevent phishing emails from reaching the end users and 

authenticate inbound email using technologies like Sender Policy Framework (SPF), 

Domain Message Authentication Reporting and Conformance (DMARC), and 

DomainKeys Identified Mail (DKIM) to prevent email spoofing. 

• Scan all incoming and outgoing emails to detect threats and filter executable files from 

reaching end users.

• Configure firewalls to block access to known malicious IP addresses.

• Patch operating systems, software, and firmware on devices. Consider using a 

centralized patch management system. 

• Set anti-virus and anti-malware programs to conduct regular scans automatically. 

• Manage the use of privileged accounts based on the principle of least privilege: no 

users should be assigned administrative access unless absolutely needed; and those 

with a need for administrator accounts should only use them when necessary. 

 

1 For additional information on Avoiding Social Engineering and Phishing Attacks, please see US-CERT Security 

Tip (ST04-014), available at: https://www.us-cert.gov/ncas/tips/ST04-014
Protecting Your Networks from Ransomware

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• Configure access controls—including file, directory, and network share permissions—

with least privilege in mind. If a user only needs to read specific files, the user should 

not have write access to those files, directories, or shares. 

• Disable macro scripts from office files transmitted via email. Consider using Office 

Viewer software to open Microsoft Office files transmitted via email instead of full office 

suite applications. 

• Implement Software Restriction Policies (SRP) or other controls to prevent programs 

from executing from common ransomware locations, such as temporary folders 

supporting popular Internet browsers or compression/decompression programs, 

including the AppData/LocalAppData folder. 

• Consider disabling Remote Desktop protocol (RDP) if it is not being used.

• Use application whitelisting, which only allows systems to execute programs known and 

permitted by security policy. 

• Execute operating system environments or specific programs in a virtualized 

environment. 

• Categorize data based on organizational value and implement physical and logical 

separation of networks and data for different organizational units. 

Business Continuity Considerations 

• Back up data regularly. Verify the integrity of those backups and test the restoration 

process to ensure it is working. 

• Conduct an annual penetration test and vulnerability assessment. 

• Secure your backups. Ensure backups are not connected permanently to the computers 

and networks they are backing up. Examples are securing backups in the cloud or 

physically storing backups offline. Some instances of ransomware have the capability to 

lock cloud-based backups when systems continuously back up in real time, also known 

as persistent synchronization. Backups are critical in ransomware recovery and 

response; if you are infected, a backup may be the best way to recover your critical 

data. 

What to Do If Infected with Ransomware

Should preventive measures fail, the USG recommends that organizations consider taking the 

following steps upon an infection with ransomware: 

• Isolate the infected computer immediately. Infected systems should be removed 

from the network as soon as possible to prevent ransomware from attacking network or 

share drives. 

• Isolate or power-off affected devices that have not yet been completely corrupted. 

This may afford more time to clean and recover data, contain damage, and prevent 

worsening conditions.
Protecting Your Networks from Ransomware

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• Immediately secure backup data or systems by taking them offline. Ensure 

backups are free of malware.

• Contact law enforcement immediately. We strongly encourage you to contact a local 

field office of the Federal Bureau of Investigation (FBI) or U.S. Secret Service 

immediately upon discovery to report a ransomware event and request assistance.

• If available, collect and secure partial portions of the ransomed data that might 

exist. 

• If possible, change all online account passwords and network passwords after 

removing the system from the network. Furthermore, change all system passwords 

once the malware is removed from the system.

• Delete Registry values and files to stop the program from loading.

Implement your security incident response and business continuity plan. Ideally,

organizations will ensure they have appropriate backups, so their response to an attack will 

simply be to restore the data from a known clean backup. Having a data backup can eliminate

the need to pay a ransom to recover data. 

There are serious risks to consider before paying the ransom. USG does not encourage 

paying a ransom to criminal actors. However, after systems have been compromised, whether 

to pay a ransom is a serious decision, requiring the evaluation of all options to protect 

shareholders, employees, and customers. Victims will want to evaluate the technical feasibility, 

timeliness, and cost of restarting systems from backup. Ransomware victims may also wish to 

consider the following factors:

• Paying a ransom does not guarantee an organization will regain access to their data; in 

fact, some individuals or organizations were never provided with decryption keys after 

paying a ransom. 

• Some victims who paid the demand were targeted again by cyber actors.

• After paying the originally demanded ransom, some victims were asked to pay more to 

get the promised decryption key.

• Paying could inadvertently encourage this criminal business model. 

How Law Enforcement Can Help

Any entity infected with ransomware should contact law enforcement immediately. Law 

enforcement may be able to use legal authorities and tools that are unavailable to most 

organizations. Law enforcement can enlist the assistance of international law enforcement 

partners to locate the stolen or encrypted data or identify the perpetrator. These tools and 

relationships can greatly increase the odds of successfully apprehending the criminal, thereby

preventing future losses. 
Protecting Your Networks from Ransomware

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Federal law enforcement places a priority on conducting cyber investigations in a manner that 

causes minor disruption to a victim entity’s normal operations and seeks to work cooperatively 

and discreetly with that entity. Federal law enforcement uses investigative measures that avoid 

unnecessary downtime or displacement of a company’s employees. Federal law enforcement

closely coordinates its activities with the affected organization to avoid unwarranted disclosure 

of information. 

As an affected entity recovers from a cybersecurity incident, the entity should initiate measures 

to prevent similar incidents. Law enforcement agencies and the Department of Homeland 

Security’s National Cybersecurity and Communications Integration Center can assist 

organizations in implementing countermeasures and provide information and best practices for

avoiding similar incidents in the future. Additionally, the affected organization should conduct a 

post-incident review of their response to the incident and assess the strengths and 

weaknesses of its incident response plan.

Ransomware Variants2

Ransomware is a growing criminal activity involving numerous variants. Since 2012 when 

police locker ransomware variants first emerged, ransomware variants have become more 

sophisticated and destructive. Some variants encrypt not just the files on the infected device, 

but also the contents of shared or networked drives, externally attached storage media 

devices, and cloud storage services that are mapped to infected computers. These variants 

are considered destructive because they encrypt users’ and organizations’ files, and render 

those files useless until a ransom is paid. 

Recent federal investigations by the FBI reveal that ransomware authors continue to improve 

ransomware code by using anonymizing services like “Tor 3” for end-to-end communication to 

infected systems and Bitcoin virtual currency to collect ransom payments. Currently, the top

five ransomware variants targeting U.S. companies and individuals are CryptoWall, CTBLocker, TeslaCrypt, MSIL/Samas, and Locky. New ransomware variants are continually 

emerging. 

CryptoWall

CryptoWall and its variants have been actively used to target U.S. victims since April 2014. 

CryptoWall was the first ransomware variant that only accepted ransom payments in Bitcoin. 

The ransom amounts associated with CryptoWall are typically between $200 and $10,000. 

Following the takedown of the CryptoLocker botnet, CryptoWall has become the most 

successful ransomware variant with victims all over the world. Between April 2014 and June 

 

2 For more information on Ransomware variants and other resources, visit https://www.uscert.gov/ncas/alerts/TA16-091A 3 Tor is free software for enabling anonymous communication. Tor directs Internet traffic through a free, 

worldwide, volunteer network consisting of more than 7,000 relays to conceal a user’s location and usage from 

anyone conducting network surveillance or traffic analysis. (The name derives from the original software project 

name, The Onion Router.)
Protecting Your Networks from Ransomware

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2015, IC3 received 992 CryptoWall-related complaints, with victims reporting losses totaling 

over $18 million.4 CryptoWall is primarily spread via spam email but also infects victims 

through drive-by downloads5 and malvertising6. 

CTB-Locker

CTB-Locker emerged in June 2014 and is one of the first ransomware variants to use Tor for 

its C2 infrastructure. CTB-Locker uses Tor exclusively for its C2 servers and only connects to 

the C2 after encrypting victims’ files. Additionally, unlike other ransomware variants that utilize 

the Tor network for some communication, the Tor components are embedded in the CTBLocker malware, making it more efficient and harder to detect. CTB-Locker is spread through 

drive-by downloads and spam emails.

TeslaCrypt

TeslaCrypt emerged in February 2015, initially targeting the video game community by 

encrypting gaming files. These files were targeted in addition to the files typically targeted by 

ransomware (documents, images, and database files). Once the data was encrypted, 

TeslaCrypt attempted to delete all Shadow Volume Copies and system restore points to 

prevent file recovery. TeslaCrypt was distributed through the Angler, Sweet Orange, and 

Nuclear exploit kits.

MSIL or Samas (SAMSAM)

MSIL or Samas (SAMSAM) was used to compromise the networks of multiple U.S. victims, 

including 2016 attacks on healthcare facilities that were running outdated versions of the 

JBoss content management application. SAMSAM exploits vulnerable Java-based Web 

servers. SAMSAM uses open-source tools to identify and compile a list of hosts reporting to 

the victim’s active directory. The actors then use psexec.exe to distribute the malware to each 

host on the network and encrypt most of the files on the system. The actors charge varying 

amounts in Bitcoin to provide the decryption keys to the victim.

Locky

In early 2016, a destructive ransomware variant, Locky, was observed infecting computers 

belonging to businesses globally, including those in the United States, New Zealand, Australia, 

Germany and the United Kingdom. Locky propagates through spam emails that include 

malicious Microsoft Office documents or compressed attachments (e.g., .rar, .zip) that were 

previously associated with banking Trojans such as Dridex and Pony. The malicious 

attachments contain macros or JavaScript files to download the Locky files. Recently, this 

ransomware has also been distributed using the Nuclear Exploit Kit.

 4 This number includes additional costs incurred by the victim. Expenses may be associated with network 

mitigation, network countermeasures, loss of productivity, legal fees, IT services, and the purchase of credit 

monitoring services for employees or customers. 5 Drive by download” is the transfer of malicious software to the victim’s computer without the knowledge of or any 

action by the victim. 6 “Malvertizing,” is the use of malicious ads on legitimate websites. These malicious ads contain code that will 

infect a user’s computer without any action from the user (i.e., the user does not have to click on the ad to 

become infected).
Protecting Your Networks from Ransomware

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Links to Other Types of Malware

Systems infected with ransomware are also often infected with other malware. In the case of 

CryptoLocker, a user typically was infected by opening a malicious attachment from an email. 

This malicious attachment contained Upatre, a downloader, which infected the user with 

GameOver Zeus. GameOver Zeus was a variant of the Zeus Trojan used to steal banking 

information and other types of data. After a system became infected with GameOver Zeus, 

Upatre would also download CryptoLocker. Finally, CryptoLocker encrypted files on the 

infected system and demanded a ransom payment. 

The disruption operation against the GameOver Zeus botnet also affected CryptoLocker, 

demonstrating the close ties between ransomware and other types of malware. In June 2014, 

an international law enforcement operation successfully weakened the infrastructure of both 

GameOverZeus and CryptoLocker.
Protecting Your Networks from Ransomware

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Federal Government Resources

Reporting

Federal Bureau of Investigation

Cyber Task Forces

www.fbi.gov/contact-us/field

Internet Crime Complaint Center

www.ic3.gov 

United States Secret Service

Electronic Crimes Task Force

www.secretservice.gov/investigation/#field 

Local Field Offices

www.secretservice.gov/contact/ 

Mitigation 

Department of Homeland Security

United States Computer Emergency Readiness Team (US-CERT)

www.us-cert.gov 

NIST Cybersecurity Framework: 

http://www.nist.gov/cyberframework/ 

NSA/IAD Top 10 Information Assurance Mitigations Strategies:

https://www.iad.gov/iad/library/ia-guidance/iads-top-10-information-assurance-mitigationstrategies.cfm