The Kraken Botnet is a network of "zombie" computers that have been infected with the Kraken trojan horse, which is a type of computer virus. Botnets like this one infect many computers worldwide with a virus that allows a remote user to control them. This lets malicious programmers use the computers of unsuspecting users for various purposes; in this case, the Kraken botnet is used to send out over 500,000 spam e-mail messages a day. That number is likely to grow since the Kraken botnet is infecting new computers everyday at a very high rate. It is already the largest botnet to date, twice the size of the previous record-holder, the Storm botnet.

The virus that makes a computer a Kraken zombie is reportedly invisible to antivirus software, and has infected the networks of 50 or more Fortune 500 companies. The virus is typically distributed as hidden information in a common image file. When the image is viewed, the virus infects the computer and allows access to the virus authors. In addition to sending out spam email, a botnet could cull the personal information stored on zombie computers, attempt to hack another server using brute force attacks, or shut down a server by flooding it with requests.