LinkedIn is believed to have suffered a password hash breach (updated: LinkedIn has confirmed the breach), thanks to a forum post that quickly caught the attention of security researchers on Twitter and other social outlets. The posted archive contained a 270+ MB text file of SHA-1 hashes, and forum discussions suggested that it was related to the popular business-centric social site.
At the moment, little is known and speculation is running wild. LinkedIn has not finished investigating whether they have been breached, however many security pros are confirming for the media that the SHA-1 hashes of their passwords are found in the file. The file is constructed in a hash-per-line fashion, with no evident plaintext that suggests it is anything other than passwords (such as usernames, etc.). However, it’s possible that anyone gaining the original access to hashes had or has access to additional details.
I obtained a copy of the hash list, produced a SHA-1 hash of my old LinkedIn password, and did indeed find it in the list. I have also spot-checked several other hashes posted by security pros on Twitter, and have found them as well. Given the nature of my own password (16 random characters comprised of A-Z, a-z, and 0-9) the likelihood that my SHA-1 hash of my password (that was unique to LinkedIn) would be present in a file that did NOT come (at least in part) from a source that had access to hashes of LinkedIn passwords is statistically impossible.