Business networking website LinkedIn has admitted that a data breach has compromised the passwords of some of its users.
In a post on the California-based website’s blog on Wednesday, Vicente Silveira, director at LinkedIn, said some passwords had been “compromised” and the situation was being investigated.
He said users whose accounts had been affected would find that their passwords were no longer valid, and would receive an email instructing them how to reset their passwords.
"We sincerely apologise for the inconvenience this has caused our members. We take the security of our members very seriously," he said.
LinkedIn has more than 161 million users worldwide, with almost two-thirds located outside the United States.
LinkedIn has a lot of information on its members, including potentially confidential information related to jobs being sought. Companies, recruiting services and others have accounts alongside individuals who post resumes and other professional information.
Later on Wednesday, online dating service eHarmony said the passwords of a "small fraction" of its users had been compromised. The site, which says it has more than 20 million registered online users, did not say how many had been affected.
Computer security experts discovered files with more than six million scrambled passwords on Tuesday, which they originally suspected belong to LinkedIn members because some of the passwords included the phrase "LinkedIn," said Graham Cluley, a senior technology consultant with British computer security software maker Sophos.
There is added concern that many people use the same password on multiple websites, so whoever stole the data could use the information to access Gmail, Amazon, PayPal and other accounts, Cluley said.
"All that's been released so far is a list of passwords and we don't know if the people who released that list also have the related email addresses," he said. "But we have to assume they do. And with that combination, they can begin to commit crimes."
The data was found on underground websites where criminal hackers frequently exchange stolen information, including scrambled passwords. It is not known who was behind the attack.
Marcus Carey, security researcher at Boston-based Rapid7, said he believed the attackers had been inside LinkedIn's network for at least several days, based on an analysis of the type of information stolen and quantity of data posted on the forums.
"While LinkedIn is investigating the breach, the attackers may still have access to the system," Carey warned. "If the attackers are still entrenched in the network, then users who have already changed their passwords may have to do so a second time."
Just a day earlier, LinkedIn was subject to criticism by a security firm for allowing too much information to be revealed from its mobile application.
LinkedIn claims to operate the world's largest professional network with members in 200 countries. It went public last year, and its share price has since doubled.