The Kraken botnet was the world's largest botnet as of April 2008[update]. Researchers say that Kraken infected machines in at least 50 of the Fortune 500 companies and grew to over 400,000 bots. It was estimated to send 9 billion spam messages per day. Kraken botnet malware may have been designed to evade anti-virus software, and employed techniques to stymie conventional anti-virus software.
In April 2008, Damballa released instructions for removing Kraken malware from computers and a list of IPs comprising the Kraken botnet. The list shows that on April 13, 2008, there were 495,000 computers in the Kraken botnet.