Millions of passwords, credit card numbers and other personal information may be at risk because of a major breakdown in Internet security revealed this week.The damage caused by the Heartbleed bug is unknown. The security hole exists on a vast number of Web servers and went undetected for more than two years. While it’s conceivable that hackers never discovered the flaw, it’s nearly impossible to tell.People can’t do much to protect themselves until the affected websites implement a fix.Here are answers to common questions about Heartbleed: What is Heartbleed and why is it a big deal?Heartbleed affects the encryption technology designed to protect online accounts for email, instant messaging and e-commerce. It was discovered by researchers from the Finnish security firm Codenomicon, along with a Google researcher working separately.It’s unclear whether any information has been stolen as a result of Heartbleed, but security experts are particularly worried about the bug because it went undetected for more than two years. How does it work?Heartbleed creates an opening in SSL/TLS, an encryption technology marked by the small padlock and “https:” on Web browsers to show that traffic is secure. The flaw makes it possible to snoop on Internet traffic even if the padlock is closed. Interlopers can also grab the keys for deciphering encrypted data without the website owners knowing the theft occurred. So if the problem has been identified, it’s been fixed and I have nothing to worry about, right?It depends on the website. A fixed version of OpenSSL has been released, but it’s up to the individual website administrators to put it in place.Yahoo, which has more than 800 million users worldwide, said Tuesday that most of its popular services — including sports, finance and Tumblr — have been fixed but that work continues on other products that it didn’t identify. So what can I do to protect myself?Ultimately, you’ll need to change your passwords, but that won’t do any good until the sites you use adopt the fix. It’s also up to the Internet services affected by the bug to let users know of the potential risks and encourage them to change passwords. I plan to file my income taxes online. Is that safe considering how much personal information is involved?The IRS released a statement Wednesday saying that it’s not affected by the bug or aware of any related security flaws. It advised taxpayers to continue filing their returns in advance of Tuesday’s deadline.But Canada’s tax agency temporarily cut off public access to its electronic filling services Wednesday, just three weeks before its tax deadline, citing Heartbleed-related concerns. The Canada Revenue Agency said it’s working to restore secure access.