About a year ago, a routine enterprise security analysis turned up 75 gigabytes of stolen data. Thus began the discovery of the ‘Kneber botnet’, which had hijacked 74,000 computers at more than 2,500 organizations around the world.

Operating undetected for a year, the Kneber botnet’s 74,000 ‘zombies’ stole 68,000 corporate logins to e-mail accounts, online banking accounts, and a variety of public email and social networking sites. It also grabbed nearly 2,000 SSL certificate files used to secure the likes of online banking transactions.

Why was this botnet able to steal so much for so long? Because less than 10% of antivirus software could recognize the sophisticated Kneber malware. Nor was it spotted by existing intrusion detection systems.

Which is the whole idea of stealth malware. Our experience shows that as many as 50% to 60% of the organizations infected like this don’t even understand it’s happening.

There are now some five million spam-sending botnets controlling 50-100 million PCs worldwide. They accounted for more than three-quarters of all spam in 2010. Besides launching distributed denial-of-service (DDOS) attacks, they’re increasingly used to exploit all manner of yet-to-be-recognized zero-day vulnerabilities in popular applications as well as mobile devices and even programmable logic controllers.

Don’t wait to be victimized. Find out what you can do to protect your business from attack.