A cyber attack that began in late 2008 was discovered last month and is believed to have hacked more than 75,000 computer systems at almost 2,500 businesses in the United States and around the world, a Virginia-based computer security firm announced today.

According to the Washington Post, the attack was one of the largest and most sophisticated attacks by cyber criminals ever discovered.

A dangerous new botnet nicknamed the “Kneber Botnet,” which was discovered by NetWitness Corp., targeted educational institutions, energy firms, financial companies and 10 government agencies.

More than half of the machines that were infected with Kneber were also infected with another botnet nicknamed Waledac. This suggests the possibility of cross-crew collaboration in the criminal underground.

The botnet allows hackers to gather login credentials to online financial systems, social networking sites and e-mail systems, and to break into accounts, steal corporate and government information and replicate identities.

The attacks were carried out by enticing employees at the targeted businesses to download infected software, or through e-mails that had infected attachments. The malicious software that was then on those employees’ computers allowed hackers to seek out passwords for things such as social networking sites and online bank accounts.

“These large-scale compromises of enterprise networks have reached epidemic levels,” said Amit Yoran, CEO of NetWitness and former director of the National Cyber Security Division, in a press release. “Cyber criminal elements let the Kneber crew quietly and diligently target and compromise thousands of government and commercial organizations across the globe.”

Yoran said conventional malware protection and signature-based intrusion detection systems are inadequate for addressing this threat.

For more information about the attack, click here.