From:- Wan Nur Aisyah bt Wan Zahari 4 server virus
In computer technology, viruses are malicious software programs, a form of malware. By definition, viruses exist on local disk drives and spread from one computer to another through sharing of "infected" files
Definition of virus…..
Viruses are spread mainly by these four ways:
Using a floppy diskette from a machine that has a virus.
Downloading a file from the internet (or bulletin board) that contains a virus.
Getting an e-mail attachment that contains a virus.
Installing software purchased from a store or mail warehouse. While this is the rarest of the ways, software vendors have been found to ship their software with viruses (unknown to them of course) on the installation diskettes/cd-roms.
Example of virus
Internet time theft
Virus / worm attack
Trojan Horse is a program that does something undocumented which the programmer intended, but that the user would not approve of if he knew about it According to some people, a virus is a particular case of a Trojan Horse, namely one that is able to spread to other programs A simple example of a trojan horse would be a program named "waterfalls.scr" claiming to be a free waterfall screensaver which, when run, instead would allow access to the user's computer remotely. About trojan horse
Types of Trojan horse payloads
Trojan horse payloads are almost always designed to do various harmful things, but could be harmless. They are broken down in classification based on how they breach systems and the damage they cause.
The nine main types of Trojan horse payloads are:
Data Destructive Email Sending
Proxy Trojan (disguising others as the infected computer)
FTP Trojan (adding or copying data from the infected computer)
security software disabler
denial-of-service attack (DoS)
URL trojan (directing the infected computer to only connect to the internet via an expensive dial-up connection)
Definition of salami attack
This attack is used for the commission of financial crimes
The key here is to make the alteration so insignificant that in a single case it would go completely unnoticed, e.g. a bank employee inserts a program into the bank's servers, that deducts a small amount of money from the account of every customer
Why Salami Attacks Persist Computer computations are notoriously subject to small errors involving rounding and truncation, especially when large numbers are to be combined with small ones.
Computer virus can affect the computer system. It can copy itself and infect a computer without permission or knowledge of the user.