As of April 2008, the Kraken botnet, sometimes spelle Kracken is the world's second largest botnet, according to researchers at the computer security company Damballa. They state that Kraken has infected machines in at least 50 of the Fortune 500 companies and has reached the size of over 400,000 bots. It is estimated to send 9 billion spam messages per day. The Kraken botnet virus may have been designed to evade anti-virus software, and is apparently virtually undetectable to conventional anti-virus software.