The most action significant in recent times was against the infrastructure behind the Rustock botnet in March 2011, which . In addition to similar campaigns against Waledec and last summer's anti-Kelihos operation, this has helped reduce the volume of spam circulating on the Internet almost back to levels last seen some years ago.

What of Zeus and why has it become so significant? The simplest answer to this is probably that it is the first banking malware to be turned into what is termed 'crimeware', that is a featured crime platform sold to criminals across the world. That has fuelled its popularity and success.

Any action that removes some of the infrastructure will have a short-term impact on its activity but the biggest blow is simply that someone, anyone, has done something. Cybercriminals profiting from effective but common malware such as Zeus have acted in the knowledge that they will probably get away with their crimes. As of today, that assumption might not be as secure.

Microsoft started in January this year.