Torjan horses
A virus that disguises itself often hidden with other software or files.
When system is carrying out one program, it secretly carries on another
Worms
It is corrupt that replicate itself within the system, moving from one file or program to another
Trap doors
An entry point to a system that bypasses normal controls
Logic bombs
A virus that is designed to start working (corrupting files or processing) when a certain event occurs.
Time bombs
A virus that is designed to start working (corrupting files or processing) on a certain date/ time
Denial of service
Rendering system unusable by legitimate users ( e.g by overloading website with millions of computer-genrated queries)