LinkedIn, criticised for inadequate network security after hackers exposed millions of its users' passwords, said on Saturday it had finished disabling all affected accounts and did not believe other members were at risk.

The company, a social network for business professionals, promised to beef up security, days after more than six million customer passwords turned up on underground sites frequented by criminal hackers.

The break-in, the latest in a string of high-profile Internet breaches around the world, has damaged the reputation of the high-flying company with more than 160 million members, and raised questions about whether LinkedIn had done enough to safeguard the private information of its users.

Some cyber security experts had warned that the company could uncover further data losses over the coming days as it tries to figure out what happened.

In its blog post, LinkedIn said it had notified all affected users, whose accounts had not been accessed, and added it did not think other users had been compromised.

"Thus far, we have no reports of member accounts being breached as a result of the stolen passwords. Based on our investigation, all member passwords that we believe to be at risk have been disabled," it said in a blog post.

"If your password has not been disabled, based on our investigation, we do not believe your account is at risk."

LinkedIn is a natural target for data thieves because the site stores valuable information about millions of professionals, including well-known business leaders.

It has hired outside forensics experts to assist as company engineers and the FBI seek to get to the bottom of the break-in. The company said on Friday it did not know if any other account information was stolen besides passwords.

However, customers whose passwords were among those stolen were still getting notified by LinkedIn as of Friday afternoon, days after news of the breach surfaced.

The way the company responds to the theft will play a critical role in determining the extent to which the incident damages LinkedIn's reputation, experts said.

LinkedIn shares rose 2.6% to $96.26 on Friday. While the breach has not appeared to hurt the stock, investors are likely watching the matter closely because the stock carries one of the loftiest valuations in technology.