Users who manage and store their passwords through password management service LastPass are being forced to change their master passwords after the site noticed an issue this week that raised the spectre of a possible security breach.

As described in a blog yesterday, LastPass (download) recently followed a string of breadcrumbs that pointed to an anomaly in its network traffic on Tuesday. Though such anomalies aren't unusual, LastPass found a matching anomaly in one of its databases. Unable to identify a root cause for either anomaly, the company made the decision to assume the worst--that some of its data had been hacked.

Although LastPass hasn't identified a specific breach, it's erring on the side of caution by now forcing its members to change their master passwords. For you non-LastPass users, what exactly does that mean

Services like LastPass and rival RoboForm let users create and manage passwords to more easily log in to the vast array of secure Web sites they visit. Those passwords can be stored on a PC or mobile device as well as online. As one means of protection, both companies typically urge users to create a single complex master password that can unlock the key to accessing their passwords. Of course, if that master password is compromised, hackers potentially can gain access to all the individual passwords, one reason why these companies advise users to employ complex master passwords.

In this case, LastPass said it believes that users with complex non-dictionary master passwords were probably safe even if any data was compromised. But the company knows that many users out of force of habit often choose simple, easily decipherable passwords. Though it sees the need to require all users to change their passwords as an overreaction, as LastPass says, "we'd rather be paranoid and slightly inconvenience you than to be even more sorry later."

In the meantime, LastPass says that it's taking further precautions against the anomaly by shutting down and moving certain key services and verifying all of its source code. The company is also enhancing the encryption used to protect its data.

Update 9:30 a.m. PT: LastPass is now reporting on its blog that the company is being overwhelmed by support requests and is having trouble keeping up with the number of password changes. The company has since set up a way for users to confirm their e-mail addresses without having to change their passwords. As a result, LastPass is urging people who are using the service from the same computer or IP address to hold off on changing their passwords for a few days.

"We're asking if you're not being asked to change your password then hold off--we're protecting everyone."

The company further suggests accessing your LastPass data offline by disconnecting from the Internet and then logging in or by downloading its LastPass Pocket software, which lets you carry around your data on a USB stick.

Update 11:07 a.m. PT: Security researchers at Duo Security have also offered their take on the LastPass security anomaly with recommendations on what LastPass users should do at this point.