File infectors virus
File infectors, also known as parasitic viruses, operate in memory and usually infect executable files. They activate every time infected files are executed: They copy themselves into other executable files and can remain in memory long after the virus has activated.
Thousands of different files infecting viruses exist, but similar to boot sector viruses, the vast majority operate in DOS 16-bit environment. A simple method of removing file infector virus is by using antivirus software to scan and clean it. However, you cannot clean system files files under Windows because they are locked in Windows mode. In this case, you have to boot your computer to DOS mode and then run the anti-virus software to clean the infected files.