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Definition of Viruses, worms and trojan horses

Definition of Viruses, worms and trojan horses - Trapdoor...

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Definition of Viruses, Worms and Trojan Horses (you can find more detail in “Network security”, page 19) Trojan horse – instructions hidden inside a useful program to do bad thing, usually the malicious instructions are installed at the time the program is written. Virus – instructions that when executed, inserts copies of itself into other programs. More recently, virus hav been applied to instructions in email messages that, when executed, cause the malicious code to be sent in email to other users. (compare to Trojan horse: virus are added into program at run time) Example : replace any instruction, say the instruction at location x, by a jump to some free place in memory, say location y; then Write the virus program starting at location y; then Place the instruction that was originally at location x at the end of the virus program, followed by a jump to x+1 Worm – a program that replicates itself by installing copies of itself on other machines across a network.
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Unformatted text preview: Trapdoor – an undocumented entry point intentionally written into a program. Usually for debugging purposes. Logic bomb – malicious instructions that trigger on some event in the future, such as a particular time occurring. Zombie – malicious instructions installed on a system that can be remotely triggered to carry out attacks such as DoS. Spreading of them: These nasty things can be in a program, a post script, email, or even if a pdf document. Clever email system help them a lot. Worm scan check your contacts table and send your friend email with the worm in. Worms can also actually log into the other machine to spread them. Virus Checkers: Virus checkers don’t work well against polymorphic virus, which changes the order of its instructions....
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