Security firm Praetorian analyzed 34 million passwords that were jacked from the LinkedIn, eHarmony and Rockyou breaches, and found that 50% of all the passwords followed 13 basic structures. Over 20 million passwords in the sample have a structure within the top 13 masks. This lack of entropy makes it possible to use statistical analysis to make cracking faster and more effective. Part of the problem is with the websites themselves, as they just require one upper case letter or number. The result is that many sites falsely mark passwords as “strong” that could be cracked in a matter of minutes.