Microsoft blamed human error after two computers on its network were hacked and then misused by spammers to promote questionable online pharmaceutical websites.

Microsoft launched an investigation, after the problem was first reported in the Register. "We have completed our investigation and found that two misconfigured network hardware devices in a testing lab were compromised due to human error," Microsoft said. "Those devices have been removed."

After they were compromised, the two servers were to handle the DNS of more than 1,000 fraudulent pharmaceutical websites, according to Ronald Guilmette, the managing member of network security software vendor Infinite Monkeys. He discovered the hacked Microsoft systems late last week while researching pharmaceutical spam. "This same group has hijacked quite a lot of machines all over the world," Guilmette said.

The devices that got hacked were "network devices that run a Linux kernel," Microsoft said.

In addition to spam, at least one of the Microsoft computers was also used to launch a denial of service attack against a website belonging to Brian Krebs. Krebs believes that Russian-based pharmaceutical spammers were behind the attack on his site.

No customer data or production systems were affected by the attack, Microsoft said.

Microsoft has taken steps to improve its security in recent years, and has taken a hard-line stance against spam, so it's embarrassing to have company systems misused in this way.

"We are taking steps to better ensure that testing lab hardware devices that are Internet accessible are configured with proper security controls," Microsoft said.

See also: Microsoft's MSRT antivirus now detects Zeus