System infectors

The system infector infects application program. These viruses may attach themselves to any executable file, with the extension .BIN, .COM, .EXE, .DRV (driver) and .SYS (device driver). These viruses take control after the initial use of the infected programs. Once the infected program is executed, the virus remains there in the RAM (Random Access Memory), even if the file is closed. When you execute another new file the virus attaches itself from the main memory in the new file. In this way all the files get infected. These types of viruses modify the content of the executable files or they may also overwrite, so it disturbs the file from executing. Some examples of system infectors are .Acid rain, Alien.298, Crazy A, etc.