A confounding computer bug called "Heartbleed" is causing major security headaches across the Internet as websites scramble to fix the problem and Web surfers wonder 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 two years. They fear the possibility that computer hackers may have been secretly exploiting the problem before its discovery.
Although there is now a way to close the security hole, there are still plenty of reasons to be concerned, said David Chartier, CEO of Codenomicon, a Finnish security firm that diagnosed Heartbleed. "I don't think anyone that had been using this technology is in a position to definitively say they weren't compromised."
Computer security experts are advising people to consider changing all their online passwords.
"I would change every password everywhere because it's possible something was sniffed out," said Wolfgang Kandek, chief technology officer for Qualys, a maker of security-analysis software. "You don't know because an attack wouldn't have left a distinct footprint."
But changing the passwords won't do any good, these experts said, until the affected services install the software released Monday to fix the problem. That puts the onus on the Internet services affected by Heartbleed to alert their users to the potential risks and let them know when the Heartbleed fix has been installed so they can change their passwords.
So far, very few websites have acknowledged being afflicted by Heartbleed, although the bug is believed to be widespread. "This is going to be difficult for the average guy in the streets to understand, because it's hard to know who has done what and what is safe," Chartier said.
Yahoo, which has 800 million users worldwide, is among the services that could be potentially hurt by Heartbleed. The company said most of its most popular services — including sports, finance and Tumblr — had been fixed, but work was still being done on other products.
Heartbleed creates an opening in SSL/TLS, an encryption technology marked by the small, closed padlock and "https:" on Web browsers to signify that traffic is secure.
The flaw makes it possible to snoop on Internet traffic even if the padlock had been closed.
In a Tuesday post announcing it had installed the Heartbleed fix, Tumblr offered its users some blunt advice.
"This still means that the little lock icon (HTTPS) we all trusted to keep our passwords, personal emails, and credit cards safe, was actually making all that private information accessible to anyone who knew about the exploit," Tumblr said. "This might be a good day to call in sick and take some time to change your passwords everywhere — especially your high-security services like email, file storage, and banking, which may have been compromised by this bug."