That data is being used to target Monster.com users with credible phishing mail that plants malware on their personal – or corporate - computers.

According to Symantec Corp, a Trojan horse called Infostealer.Monstres has stolen more than 1.6 million records belonging to Monster Worldwide Inc’'s job search service. The personal information includes names, e-mail addresses, home address, phone numbers and resume identification numbers.

It worked by using legitimate log-ins from Monster.com, most likely stolen from recruiters and human resource personnel who have access to the "Monster for employers" areas of the site.

Once inside, the Trojan horse ran automated searches for resumes of candidates located in certain countries or working in certain fields. The results were then uploaded to the attackers' remote server.

Hackers then tried to infect the computers of candidates by sending targeted Monster.com phishing mails which install malware.

The first piece of malware, dubbed Banker.c by Symantec, is an information-stealing Trojan horse that monitors the infected PC for log-ons to online banking accounts.

When it notices a log-on in process, Banker.c records the username and password and transmits the data back to the hackers.

Gpcoder.e is a Trojan horse that encrypts files on the hacked computer, then holds those files hostage until the user pays a fee to unlock the data.