A computer security breach at Oak Ridge National Laboratory, in which hackers stole a database of visitors' personal information, was a highly sophisticated cyberattack and part of a concerted effort to penetrate numerous U.S. labs and other scientific facilities reports, United Press International (UPI).

Although the identity of the attackers remains unclear, security researchers have linked some Internet addresses recently used in similar attacks to computers in China.

In an e-mail message sent to staff, Oak Ridge Director Thom Mason said the breach "now appears to be part of a coordinated attempt to gain access to computer networks at numerous laboratories and other institutions across the country."

A spokesman for the Los Alamos National Laboratory told UPI that "a very small number, single figures," of the lab's unclassified computers had been compromised in a "malicious, sophisticated hacking" attack last month.

"The investigation is continuing," said the spokesman, Kevin Roark. He declined to comment on whether the attack was linked to the one on Oak Ridge.

Mason said the Oak Ridge hackers made more than 1,000 attempts to steal data "with a very sophisticated strategy" involving the use of highly targeted so-called spear phishing e-mails, "all of which at first glance appeared legitimate."

Phishing e-mails classically purport to come from a bank or other financial institution of which the target is a customer, reports UPI. They tell the recipient to go to a Web page to "confirm" their login and password, but the link in the e-mail instead directs them to a hacker site where their information is used to break into their account and steal their money.

"Phishing attacks are very problematic" for information security professionals, former Energy Department cybersecurity chief Bruce Brody told UPI.

"They exploit the weakest link in the system, the user," Brody says. "If done with even a little sophistication, it is almost impossible to protect the entire population" of system users from such attacks.

Spear phishing attacks are even harder to defend against, because they combine such e-mails with so-called social engineering techniques -- using known information about the target to personalize the attacks. The embedded link or attachment will often install software on the target's computer that steals their logins and passwords for multiple sites or systems they use.

In the Oak Ridge attack, the hackers used seven kinds of e-mail, Mason says. One purported to advise staff about a scientific conference organized by the Department of Defense (DoD), while another pretended to be notification of a complaint to the Federal Trade Commission (FTC).

"At present we believe that about 11 staff opened the attachments, which enabled the hackers to infiltrate the system and remove data," Mason wrote in the message. In a separate notice posted on its Web site, the lab stated that the first breach occurred Oct. 29.

The notice said the data stolen included a database of visitors to the top-security site, which houses a nuclear research reactor and the lab that does scientific work on a number of national security issues for the Department of Energy (DoE).

"If you visited (the lab) between the years 1990 and 2004 your name and other personal information such as your social security number or date of birth may have been part of the stolen information," reads the notice, which advises visitors to monitor their credit records for possible identity theft or other fraud.

The message said there was no evidence that any of the information stolen had been used by hackers, and some observers were skeptical that the entire penetration had been devised simply to steal that kind of data.

"It could be a target of opportunity," former Justice Department cybercrime chief Mark Rasch told UPI. "Once they (the hackers) were in there, they took whatever they could get."

On the other hand, he said, if the attack were from a foreign intelligence service, "It might be useful to know who had visited" a classified facility, if only as "a source of leads about who might have access to classified information."

National laboratories like Oak Ridge "have historically been lucrative targets for foreign intelligence services," Brody says.