Account Bruteforce is a mode that hackers use to crack someone's user and password information. Currently only few hacking groups use it, because it's hard to implement into websites. Account Bruteforce can be only used on websites.
The developing of Account Bruteforce
It was developed during 2008 and 2009, and it became more popular this year. Account Bruteforce works only on MSN, Facebook, Myspace, and Skype because of their easy-friends managing. It works by logging in with your user account. Than the server takes information from all of your friends, and starts a Bruteforce hacking method.
Is it safe?
It is safe because all of your information is encrypted with 128 bit encryption.