Social networking website LinkedIn is investigating claims that over six million of its users' passwords have been leaked onto the internet.

Hackers posted a file containing encrypted passwords onto a Russian web forum.

They have invited the hacking community to help with decryption.

LinkedIn, which has over 150 million users, has not released a formal statement, but tweeted: "Our team is currently looking into reports."

Later, it added: "Our team continues to investigate, but at this time we are still unable to confirm that any security breach has taken place."

Security researcher Graham Cluley told the BBC he believed the breach was genuine.

"We've confirmed there are LinkedIn passwords in the data.

"We did this by searching through the data for (hashed) passwords that we at Sophos use only on LinkedIn. We found those passwords in the data. We also saw that hundreds of the passwords contain the word 'Linkedin'.

"Our advice is to change your LinkedIn password. And if you use the same password on other accounts, change it there too."

BBC News