Malware is software designed specifically with the goal of executing unwanted and usually damaging functions. Common types of malware include, among others, viruses, worms, and Trojan horses. Malware is usually activated in secret without the knowledge or permission of the user.

These days, malware provides an attacker with extensive communication and control capabilities, as well as a number of functions. Among other purposes, malware may be used to obtain specific passwords, control systems remotely, disable protective software and collect data without authorisation.

The most serious damage that can be caused by malware is the loss or corruption of information or applications. However, the image loss and financial damage that can result from malware can also be significant.

Examples:

• In the past the W32/Bugbear malware spread in two ways: it searched local networks for computers with shares with write access and copied itself to them. In addition, it sent itself in an e-mail in HTML format to the recipients in the e-mail address book of the computers it infected. Due to an error in the HTML routine of certain e-mail programs, the malware was executed when the message was opened without requiring any action by the recipient.
• The W32/Klez worm spread different versions of itself. Infected computers sent the virus to all recipients in the address book of these computers. Once this virus infected a computer, it prevented all further attempts to install commonly available anti-virus software by continuously manipulating the operating system. The continuous manipulation of the operating system made disinfecting the infected computer significantly more difficult.

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