However, there is a minority of these viruses that are very destructive and will attempt to format the hard drive at a pre-determined time, or perform some other malicious action. Most often, infection by these viruses can be noted by a growth in file size from its uninfected size. In many cases, the virus can be successfully removed from the infected file, although if the virus has overwritten part of the program's code the file will be unrecoverable. AIDS552 is a file infecting virus. It infects EXE files only.
Infections occur when an infected file is executed.
The virus then loads its viral program into memory. Once memory resident, AIDS552 will infect any EXE files accessed. This is a Trojan horse. A trojan is a program which does something malicious when executed. Unlike a virus, a trojan will not replicate by infecting other files.