According to Google
Clickbot.A is the name of a botnet that Google’s Click Quality and Security Teams investigated last year. Using our findings, we published “The Anatomy of Clickbot.A” – a detailed case study on botnet-based click fraud for the benefit of the technical research community.
Clickbot.A is an example of a botnet operator attempting a click fraud attack against syndicated search engines. Google was able to identify clicks on our advertisers’ ads that exhibited Clickbot.A-like patterns and flagged them as invalid. While Clickbot.A is a specific example of a botnet application that conducted click fraud, botnets can also be used for keylogging, distributed denial of service (DDoS), and other types of attacks.
Due to the potential for misuse and the inherent loss of control that can result from having a machine participate in such a botnet, we hope “The Anatomy of Clickbot.A” will help facilitate further collaboration between search engines, Internet Service Providers (ISPs), anti-virus vendors, and other parties on the Internet in managing botnets and similar threats.
You can download the white-paper study from the Google Adwords Blog