The master boot sector is the first place your system reads from when booting up from the hard drive. Then, whenever the computer is booted up, the virus will be loaded into the system's memory. Program or file viruses are pieces of viral code that attach themselves to executable programs. Once the infected program is run, the virus is transferred to your system's memory and may replicate itself further. Macro viruses are viruses that infect documents run by applications, that use macro languages, like Microsoft Word, Excel, and Outlook.
Multipartite viruses have characteristics of both boot sector viruses and file viruses.
They may start out in the boot sector and spread to applications, or vice versa. Net Bus, Back Orifice, and Sub Seven can also be subcategorized as a Trojan Horse virus. The default name of the virus is server.exe, if someone tries to send you server.exe don't accept it. These viruses are easier to find on the net, and even easy to use. These viruses are not active until victims run what they think is a game, anti-virus program, or whatever the infector told the victim it is.