4. Anonymous Takes Down HBGary Barr 

Date: February 6-11, 2011 
Victim: HBGary Federal, Aaron Barr 

After claiming to have infiltrated Anonymous, HBGary Barr and its CEO Aaron Barr got hit with one of the hacker group's strongest attacks to date. Anonymous first took over the hompage of the security company and replaced it with the above letter (click here for full-sized image) which read in part: "You brought this upon yourself. You've tried to bite at the Anonymous hand, and now the Anonymous hand is bitch-slapping you in the face." 

The group went on to shut down the company's phone system and hack into the company's e-mail system, making public over 68,000 private e-mails which included presentations, information on competing firms, and info on HBGary Barr's plans on taking down WikiLeaks. It didn't stop there. The group to over Aaron Barr's Twitter account and posted his home address along with his phone number.