The virus spreads when an executable file is transferred from one PC to another.

CNN: Some Aptivas shipped with CIH virus

Then it copies itself into the Windows directory as an executable file, and is launched the next time the computer is booted.

CNN: Sasser worm rips through Internet

But the tool bar was actually an executable file which installed a Trojan virus that then displayed a fake security alert when the PC was rebooted.

BBC: Hackers website

The virus was spread by e-mail as an "executable" (.exe) file capable of running on Windows 95 and 98 operating systems.

CNN: FROM THE WEB