Barack Obama has left the presidential campaign trail and joined George W Bush, Al Qaeda and Microsoft to recruit zombies for the world's second largest botnet, Rustock.

The efforts are part of a massive coordinated spam campaign, the largest ever seen by one security researcher, to recruit new nodes into Rustock's 150,000 strong zombie army that pumps out some 30 billion e-mails a day.

The tactic is working, according to security researchers in the Marshal Trace team who report the botnet is responsible for 21.5 percent of global spam, up 11.5 percent in one month.

Rustock's spam e-mails have diversified as part of the campaign including bogus subject lines such as "Martian soil fantastic for growing weed says NASA", "Yahoo sold to Microsoft, record price" and "Bush down to 8 friends on Myspace".

The researchers claim the campaign is a success, despite that it still relies on an executable, codecinst.exe, as the vector for infection via a variety of fake news sites. The spambot can be automatically delivered to users operating unpatched Internet Explorer browsers through a JavaScript exploit.

Meanwhile, Sophos claims that attacks via email file attachments have reduced this year.

According to data from the company's research labs collected in the same period by the Trace team, malicious attachments have fallen from 0.3 percent (1:332) of legitimate e-mails to 0.04 percent (1:2500).

Sophos data claims the Pushdo Trojan is the malicious attachment of choice for spammers, accounting for 31 percent of all reports. Lucid images of Nicole Kidman and Angelina Jolie have been used to push out the malware.

The botnet campaign comes on the back of reports from Finnish security vendor F-Secure which has collected it's one millionth piece of malware.

The vendor claims 2300 new Trojans and exploits appear each day, double the number reported since the start of this year.

Sophos claims in its latest threat report that the total amount of malware in existence now exceeds 11 million.

Polymorph viruses, which adopt the signature of old viruses to obfuscate anti-virus detection, are growing faster than all other forms, according to F-Secure. Anti-virus monitors identify polymorph viruses by the piggy-backed signature, rather than the code itself, and will often only remove the known script.