Update 1:08 p.m. PT: LinkedIn confirms that passwords were "compromised."

LinkedIn users could be facing yet another security problem.

A user in a Russian forum says that he has hacked and uploaded almost 6.5 million LinkedIn passwords, according to The Verge. Though his claim has yet to be confirmed, Twitter users are already reporting that they've found their hashed LinkedIn passwords on the list, security expert Per Thorsheim said.

LinkedIn revealed through its own tweet that it's looking into reports of stolen passwords, and it advised users to stay tuned for more information.

Many of the hashes include the word "linkedin," which The Verge believes lends credibility to the reports.

LinkedIn passwords are encrypted using an algorithm known as SHA-1, which is considered very secure. Complex passwords will likely take some time to decrypt, but simple ones may be at risk.

Sophos security expert Graham Cluley is advising LinkedIn users to change their passwords as soon as possible, at least as a precaution. If the report is true, then hackers are undoubtedly working hard to decrypt the hashed, or unsalted, passwords.

"Although the data which has been released so far does not include associated email addresses, it is reasonable to assume that such information may be in the hands of the criminals," Cluley added.

The report of the leaked passwords comes hard on the heels of word from security researchers that LinkedIn's iOS app is collecting information from calendar entries -- including passwords -- and transmitting it back to the company's servers without users' knowledge.

A LinkedIn spokeswoman told CNET that the company does not use account password information for the calendar feature of its iOS and Android apps and that the initial report may have been referring instead to passcodes that are sometimes stored for dial-in meetings.

But in response to concerns over this collection of data, LinkedIn yesterday tried to explain how and why it captures this information.

The company acknowledged that it picks up information from the Calendar app on your iOS device to try to sync any appointments listed with fellow LinkedIn users. The feature is opt-in, so users of the LinkedIn IOS app can turn off the ability to "Add Calendar" in the Settings screen.

The details sent to LinkedIn's server include the e-mail addresses of the people you meet with, the meeting subject, the location, and any meeting notes. The calendar data is sent securely using SSL encryption and isn't shared or stored, LinkedIn added.

But in a concession to concerned users, the company has promised two tweaks to the feature. It will no longer pick up meeting notes from your calendar. And it will add a "learn more" link to explain how your calendar data is being used.

To change your LinkedIn password, log onto your account. Click on your name in the upper right corner and then click on the link for Settings. In the Settings section, click on the Change link next to Password. You'll be prompted to to enter your old password and then create a new one. Aim to pick a complex password that's not easy to decipher. Then click on the Change Password button.

CNET contacted LinkedIn for further details and will update the story when we get more information.

Updated at 4:30 a.m. PT June 7 with response from LinkedIn on account passwords.