Last Updated Apr 9, 2014 7:00 PM EDT
News of yet another alarming lapse in Internet security has left millions of people wondering what they can do to protect their passwords, credit card numbers and other sensitive data.
The security bug known as "Heartbleed" affects the encryption technology OpenSSL, which is used by about two-thirds of Web servers to protect online accounts for email, instant messaging and electronic commerce. OpenSSL is a variant of SSL/TLS encryption, denoted by the little padlock symbol and "https:" on Web browsers to signify that traffic is secure.
The flaw makes it possible for hackers to snoop on Internet traffic despite the supposedly secure padlock, without leaving a trail, so website owners and users wouldn't even realize the theft had occurred.
"I don't think anyone that had been using this technology is in a position to definitively say they weren't compromised," said David Chartier, CEO of Codenomicon, the Finnish security firm that diagnosed Heartbleed. (A researcher from Google Inc. also independently discovered the threat.)
Computer security experts offered the following advice for users concerned about the breach:
Change your online passwords -- all of them
"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.
And follow these guidelines for choosing secure passwords. Don't use common words or a string of consecutive numbers. Experts recommend passwords be at least eight characters long, using a combination of letters, numbers and symbols. Avoid using the same user name and password for multiple sites.
Make sure Web services you use have updated their security
Changing your passwords won't do any good, experts explained, until the affected Web services install software to fix the problem. They would then need 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.
Fortunately, "many of the biggest and most important services have already been patched and fixed," Mandiant Security senior consultant William Ballenthin tells CBS News. "I've already received notices from Google and Amazon and Yahoo that they identified the issue last week and they've already fixed it."
CNET advises Web users to check the security of individual sites here, though it warns that caution is still warranted even if the site has an "all clear" indication. If you're given a red flag, avoid the site for now.
Yahoo Inc., which boasts more than 800 million users worldwide, is among the Internet services reportedly compromised by Heartbleed. Yahoo says most of its most popular services -- including sports, finance and Tumblr -- has been fixed, but work was still being done on other products that it didn't identify in a statement Tuesday.
"We're focused on providing the most secure experience possible for our users worldwide and are continuously working to protect our users' data," Yahoo said.
CNET reports that other major Web services, including Facebook, Google and Twitter, did not appear to be compromised -- but as Chartier points out, it's hard to know for sure.Keep an eye on your credit card statements
Just in case your data was breached, check your financial statements and report any suspicious activity to your credit card company.
Be cautious of smaller Web sites
Despite the worries raised by the Heartbleed bug, Codenomicon said many large consumer sites aren't likely to be affected because of their "conservative choice" of equipment and software. "Ironically, smaller and more progressive services or those who have upgraded to (the) latest and best encryption will be affected most," the security firm said in a blog post.
Although it may take months for smaller sites to install the Heartbleed fix, Chartier predicts all the major Internet services will act quickly to protect their reputations.
In the meantime, Ballenthin says, there's no need to panic. "I think really you just need to be aware that the issue's out there, and when [a Web site] asks you to reset your password, or change some settings, go ahead and do it as soon as you can."