Over the last few months, many people have talked about using HTTPS with sites such as Facebook and Twitter. The technology came up often after the release of Firesheep, which allowed Wi-Fi users to hijack other users who used these sites without HTTPS.

Part of the technology behind HTTPS are certificates – small electronic files that help your browser ensure it’s connecting to a trusted site and protect the connection from eavesdropping or tampering. For instance, when you visit https://www.google.com, the Google server has a certificate that lets your browser know it’s connecting to Google and not an impostor.

But how does your browser know if the certificate is not also from an impostor? Each browser maintains a list of certificate authorities, or CAs – special servers whose main purpose is issuing certificates for all those HTTPS websites. These CAs may also vouch for other authorities, creating a hierarchy of trust. If you access a site whose certificate is not from one of these authorities or has been marked by one of them as revoked, you’ll get an error or warning about a certificate problem. Ideally, all of the authorities are all trustworthy and only issue certificates for reputable websites.

Unfortunately, the current reality is less than ideal, and attacks can happen. Yesterday, a blog post from the Tor Project detailed research showing that two major browsers had quietly added code which blocked a few specific certificates. These certificates were issued by an authority in a hierarchy controlled by Comodo, who released a statement today providing a bit more information on what happened.

According to Comodo, attackers were able to access the account of a user who helped manage one of the servers for issuing certificates. They then created their own certificates for verifying websites from Google, Yahoo, Skype, and others. These fraudulent certificates could be used to make a user’s browser think it was connecting to legitimate sites when actually communicating with a malicious site.

Comodo stated that many of the attacks appear to be from Iran, and has said they believe the attack to be state-driven, but many details are still unknown at this point, and the situation calls into question several aspects of Comodo’s security policies. In the meantime, you should make sure you’re using the latest version of a modern browser, such as Chrome or Firefox, and avoid connecting to untrusted networks. The fraudulent certificates that have already been identified will be blocked by an updated browser, and we’ll have to wait and see if more fallout results from the attack.

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