A botnet spam virus said to comprise close to a million infected computers has been disrupted, according to a report issued Thursday by the BBC.

Security researchers said that would make it the largest ever take down of a cyber crime network. It was not clear whether the Rustock botnet was intentionally dismantled. When a botnet is disabled, it can be back up and running in days, according to security experts.

“In 2010, the Rustock botnet – a collection of infected machines – was the most prolific producer of spam on the Internet, at its peak accounting for nearly half of all spam sent globally – some 200 billion messages a day,” the BBC report said. “And new types of malware are proliferating rapidly, making it harder for computer users to ensure their systems are fully protected.”

A report issued this week by Panda Security found that in the first three months of 2011, an average of 73,000 new malware strains were identified, most of which were Trojans. There was a 26 percent increase of new threats compared to the same period last year.

“The proliferation of online tools that enable non-technical people to create Trojans in minutes and quickly set up illegal business – especially when it can provide access to banking details – is responsible for Trojans’ impressive growth,” said Luis Corrons, technical director of PandaLabs.

According to research from Symantec in its annual MessageLabs Intelligence 2010 Security Report, Rustock was responsible for more than 44 billion spam emails per day and had more than one million bots under its control. Botnets Grum and Cutwail are the second and third largest respectively, the report said.

Symantec officials predicted that in 2011 botnet controllers will resort to employing steganography techniques to control their computers. This means hiding their commands in plain view – perhaps within images or music files distributed through file sharing or social networking websites. This approach will allow criminals to surreptitiously issue instructions to their botnets without relying on an ISP to host their infrastructure—thus minimizing the chances of discovery.