BSI ID: G 0.39

A malicious program is software that has been developed with the aim of performing unwanted and usually harmful functions. Typical types of malware include viruses, worms and Trojan horses. Malware usually becomes active secretly, without the user's knowledge or consent. Nowadays, malware offers attackers extensive communication and control options and has a wide range of functions. Among other things, malware can specifically search for passwords, remotely control systems, deactivate protection software and spy on data. The damage caused here is particularly serious in the form of the loss or corruption of information or applications. However, the damage to reputation and financial loss that can be caused by malware are also significant.

Examples:

• In the past, the W32/Bugbear malware spread in two ways: it searched local networks for computers with shared folders that could be written to and copied itself onto them. It also sent itself as an HTML email to recipients in the email address book of infected computers. Due to an error in the HTML routine of certain email programmes, the malware was executed when the message was opened without any further action on the part of the recipient.

• The W32/Klez malware spread in various variants. Infected computers sent the virus to all recipients in the computer's email address book. Once this virus had infected a computer, it prevented the installation of virus protection programs from popular manufacturers by continuously manipulating the operating system, making it much more difficult to disinfect the infected computers.