The password list posted to the hacker site contained password hashes -- cryptographic representations created by a SHA-1 hash algorithm that turns passwords into a long series of characters. While SHA-1 hashes are difficult to break, especially for complex passwords that contain numbers, capital letters and special characters, they are not impossible.
As odd as it sounds, hackers use dictionaries, or literature, to try and break the hash coding in order to retrieve original passwords.
In the infographic below, security company Rapid7 has compiled a list of the top 30 LinkedIn passwords cracked by hackers along with a basic breakdown of the numbers.
Check out the graphic and, if your password was one of the ones cracked, it may be wise to heed some of the common sense security tips.