"Hackers have stolen usernames and passwords...compromising accounts at Facebook, Gmail, Twitter, Yahoo and ADP."
Article Dec 4, 2013 from CNN Money here
2 million Facebook, Gmail and Twitter passwords stolen in massive hack
The author, Jose Pagliery, said Trustwave notified the above-named companies of the breach. According to the article, '(Miller) said the team doesn't yet know how the virus got onto so many personal computers. The hackers set up the keylogging software to rout information through a proxy server, so it's impossible to track down which computers are infected. The hacking campaign started secretly collecting passwords on Oct. 21, and it might be ongoing: Although Trustwave discovered the Netherlands proxy server, Miller said there are several other similar servers they haven't yet tracked down."
Miller also was quoted, "Just searching programs and files won't be enough, because the virus running in the background is hidden."
For Best Practises to Common Security Questions, please refer to this BleepingComputer topic for guidance on safe computing, prevention of viruses and malware, and system hacks by quietman7.