Hackers have stolen usernames and passwords for nearly two million accounts at Facebook, Google, Twitter, Yahoo and others, according to a report released this week.

By Jose Pagliery  @Jose_Pagliery December 4, 2013 (CNNMoney)

The massive data breach was a result of keylogging software maliciously installed on an untold number of computers around the world, researchers at cybersecurity firmTrustwave said. The virus was capturing log-in credentials for key websites over the past month and sending those usernames and passwords to a server controlled by the hackers.

On Nov. 24, Trustwave researchers tracked that server, located in the Netherlands. They discovered compromised credentials for more than 93,000 websites, including:

• 318,000 Facebook (FB, Fortune 500) accounts
• 70,000 Gmail, Google+ and YouTube accounts
• 60,000 Yahoo (YHOO, Fortune 500) accounts
• 22,000 Twitter (TWTR) accounts
• 9,000 Odnoklassniki accounts (a Russian social network)
• 8,000 ADP (ADP, Fortune 500) accounts
• 8,000 LinkedIn (LNKD)accounts

Trustwave notified these companies of the breach. They posted their findings publicly on Tuesday.

"We don't have evidence they logged into these accounts, but they probably did," said John Miller, a security research manager at Trustwave.