SAN FRANCISCO (AP) — A confounding computer bug called "Heartbleed" is causing major security headaches across the Internet.

Websites are scrambling to fix the problem and Web surfers are pondering whether they should change their passwords to prevent theft of their email accounts, credit card numbers and other sensitive information.

The breakdown revealed this week affects a widely used encryption technology that is supposed to protect online accounts for a variety of online communications and electronic commerce.

Security researchers who uncovered the threat are particularly worried about the lapse because it went undetected for more than two years. They fear the possibility that computer hackers may have been secretly exploiting the problem before its discovery. It's also possible that no one took advantage of the flaw before its existence was announced late Monday.

Although there is now a way to close the security hole, there are still plenty of reasons to be concerned. Experts say no one can make the claim that they were not compromised.