9. Formspring Password Breach
Formspring, which specializes in providing a platform to answer user-submitted questions, had to answer questions about how hundreds of thousands of password hashes were posted to a hacker forum. The company reset the passwords to all of its 28 million users following the exposure and admitted that the breach enabled attackers to gain access to some of its account holders. The attackers gained access to one of the company's development servers and stole the data from a production database, the company said.