New answers tagged intrusion
Some breaches are publicly disclosed on PasteBin or similar sites, but these are relatively few and far between. Even if you could get a list of all e-mail addresses belonging to compromised accounts from all the data breaches, this will only help you find users who might be affected. This does nothing to tell you if your users actually used the same ...
Web security guru Troy Hunt has a site called have I been pwned? which checks an email address against those associated with a number of breaches. The passwords gleaned from the breaches are not retained there, so it's useful for determining if an account may be affected but does not disclose what the passwords or hashes were that were stolen.
I generally read technology news to keep me update about security breaches. Few are the sources I generally used and you can read archive for 2013 references. http://www.bbc.com/news/technology/ http://edition.cnn.com/TECH/ I further recommend reading 2013 Cost of Cyber Crime Study report
One option, although it focuses on dataloss as opposed to specifically security breaches, would be the data loss db. In terms of the most important breach of 2013 as mentioned in comments already that's subjective, but arguably one could suggest that the NSAs data loss was the most significant of last year
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