You cannot rely on strange behavior to find viruses. The most reliable way to find viruses is to use competent anti-virus software. Although it is possible to write a virus for virtually any computer, the viruses that are commonly spreading in the world today are limited to microcomputers. Infected files can be stored almost anywhere. Even when they cannot run on the server machine, an infected file on the server can be run by DOS machines on the network and can spread the infection to them.
Viruses are a threat, but data loss can also occur from other factors.
If you have files you can't afford to lose, make sure you have more than one copy of them. When the boot sector program is read and executed, the virus goes into memory and infects your hard drive. File Infector virus' infect uninfected programs when they are executed in memory. In other cases they are infected when they are opened, occasionally the virus simply infects all of the files in the directory it was run from. The file-infector class is also used to refer to programs that do not physically attach to files but associate themselves with program filesnames.