rogram propagates itself by modifying other programs to include a possibly changed copy of itself and that is executed when the infected program is(67). A virus often causes damage or annoyance and may be triggered by some event such as the occurrence of a predetermined date.Worm is a self-contained program that can propagate itself through data processing systems or computer networks. Worms are often designed by hackers to use up(68) resources such as storage space or processing time.Trojan horse implies by the name an apparently harmless program containing(69) logic that allows the unauthorized collection, falsification or destruction of data. Logic bomb causes damage to a data processing system when triggered by some specific system condition. Time bomb is also a malicious program being activated at a(70) time.