In computer security, a denial-of-service attack (DoS attack) is an attempt to make a computer resource unavailable to its intended users. Typically the targets are high-profile web servers, and the attack attempts to make the hosted web pages unavailable on the Internet. It is a computer crime that violates the Internet proper use policy as indicated by the Internet Architecture Board (IAB). TFN2K and Trinoo are tools used for conducting DDos attacks.

The easiest programs to trojan and the smartest ones to trojan are ones commonly run by administrators and users, in this case netstat, ps, and top, for a complete list of commonly trojaned and rootkited software please reference this URL: http://www.usenix.org/publications/login/1999-9/features/rootkits.html

Explanations: Both Pretty Park and BugBear use email to spread. Pretty Park cannot propagate via network shares, only email. BugBear propagates via network shares and email. It also terminates anti-virus applications and acts as a backdoor server for someone to get into the infected machine. Pretty Park tries to connect to an IRC server to send your personal passwords and all sorts of other information it retrieves from your PC. Pretty Park cannot terminate anti-virus applications. However, BugBear can terminate AV software so that it can bypass them.