One of the most sensitive science labs in the US has shut down all internet access after attackers exploited a vulnerability in Microsoft's Internet Explorer browser to steal data from some of its servers, according to published news reports.

The security breach at the Oak Ridge National Laboratory is at least the second time since 2007 that computers have been hacked when employees were duped by phishing emails. The most recent compromise was initiated by messages that were manipulated so that they appeared to come from the lab's Human Resource Department, The Knoxville News Sentinel reported.

According to a follow-up post, a link included in the fraudulent email, which first entered the lab's systems on April 7, exploited a critical vulnerability in IE that Microsoft fixed last Tuesday. It was the same bug that fetched a security researcher a $15,000 prize in the recent Pwn2Own hacking contest.

A lab spokesman told Security News Daily that security personnel “saw substantial activity” that resulted in “very limited data in the megabytes, not the gigabytes” being stolen.

The publication also said that of the 530 or so employees who received the email, 57 of them clicked on the booby-trapped link. It's a startling admission, given that the previous security breach was also touched off when workers clicked on malicious attachments embedded in emails that informed the recipients of an upcoming scientific conference or pretended to give information about a complaint filed on behalf of the Federal Trade Commission.

As is becoming common when malware penetrates a highly sensitive organization that should have known better, Oak Ridge National Labs blamed the breach on an “advanced persistent threat,” a buzz term that seems to mean different things to different people. RSA recently used the same phrase when disclosing an attack on its network that could compromise the security of its SecurID tokens for two-factor authentication.

A spokeswoman for the lab told Computerworld that email service was expected to be restored on Wednesday, although no attachments would be allowed for the time being. She also told the publication that several other national laboratories and government organizations were targeted in the same attacks.

Oak Ridge National Laboratories is a highly secretive facility located in Tennessee that is used for homeland security and military purposes. It is managed by the US Department of Energy and conducts research into nuclear energy, chemical science, and biological systems.

Representatives didn't return emails and calls seeking comment. ®