LinkedIn is reportedly working with the FBI to investigate a data breach that compromised as many as 6.5 million passwords.
Reuters reported that the FBI is now investigating the data theft on Friday, although a LinkedIn spokesperson refused to confirm or deny the news when asked by V3.
"We are also actively working with law enforcement, which is investigating this matter," they said.
The attack came to light when the stolen LinkedIn passwords were posted by an unnamed individual on a Russian hacker site. The data breach was subsequently confirmed by LinkedIn on Wednesday.
"We want to provide you with an update on this morning's reports of stolen passwords. We can confirm that some of the passwords that were compromised correspond to LinkedIn accounts," it said.
"We are continuing to investigate this situation."
The company confirmed that the breach had compromised at least 6.5 million users' passwords though security firm Imperva has questioned the figure, suggesting the number of passwords stolen is likely far higher.
LinkedIn has moved to calm users' concerns following the data breach assuring users that most of the passwords are still protected.
"To the best of our knowledge, no email logins associated with the passwords have been published, nor have we received any verified reports of unauthorised access to any member's account as a result of this event," it said.
The firm is one of numerous websites to have its passwords stolen by cyber criminals during a recent crime wave.
As well as LinkedIn, dating site eHarmony and music sharing site Last.fm have admitted to data breaches, issuing warnings to users that their accounts may be at risk.