The number of computers currently controlled by botnets has exploded in recent months, according to researchers.

Recent figures recorded by the Shadowserver Foundation reveal that the number of computers infected by botnets has quadrupled in the past 90 days.

The increase comes despite a slight drop in the number of botnets, leading researchers to believe that the increase has largely benefited the established operators in the field.

The increase has also come despite little to no increase in the volume of new malware and viruses being discovered in the wild.

Some researchers believe that computers are being infected through web-based attacks, specifically SQL injection.

Sans Institute researcher John Bambenek noted that the increase in botnet infections seems to coincide with the appearance of large-scale SQL injection attacks, in which hundreds of thousands of web pages are compromised with embedded exploit code.

Bambenek suggested that many security firms lack a mechanism for accurately rooting out the SQL attacks before they become widespread.

"Short of spidering the web on a consistent basis, it gets difficult to find infected sites for that malware," he said.

"It is one of the disadvantages of operating in a reactive fashion; we are behind the power curve for some time until we figure out a way to approach something close to parity."