Monster.com suffered a major data breach at the weekend, with a Trojan horse stealing more than 1.6 million records from the job search site's database.

Symantec's Security Response blog reports the Trojan, called Infostealer.Monstres, can steal sensitive information from Monster.com by using employer accounts which have presumably been compromised by an attacker.

"Such a large database of highly personal information is a spammer's dream," Symantec security analyst Amado Hidalgo wrote in the blog.

Using the stolen account, the Trojan logs into Monster.com job recruiter website and searches for all available resumes, potentially lifting the name, email address, home address and phone numbers of its victims. The program then attempts to post the stolen information on a remote server controlled by the attacker.

From Symantec's blog:

The Trojan sends HTTP commands to the Monster.com Website to navigate to the Managed Folders section. It then parses the output from a pop-up window containing the profiles of the candidates that match this recruiter's saved searches.

The security firm reports the attackers have stolen over 1.6 million entries on the site, with personal information belonging to several hundred thousand individuals, mostly based in the US.

The main file used by the Trojan is ntos.exe, an executable also commonly used by Trojan.Gpcoder.E, a similar piece of malware. The Trojans share the Monster.com logo for the executable icon - leading Symantec to speculate the same group is behind both.

Adding to the mess, Trojan.Gpcoder.E has reportedly been sent in Monster.com phishing emails. The emails use the personal information to fool users into downloading a Monster Job Seeker Tool, which is in reality, Trojan.Gpscoder.E.

This nasty executable encrypts files in the affected computer — and leaves a text file demanding the victim pay the attackers in order to recover the data.

Unfortunately, even a massive data security breach such as this one has become commonplace in recent years. Security watchgroup Privacy Rights Clearinghouse lists 18 data breaches in the US this month alone - not counting Monster.com. According to the organization, 159 million records containing sensitive personal information have been compromised in the US by security breaches since 2005.

Symantec has told Monster.com of the compromised recruiter accounts so they can be disabled. In the meantime, Symantec advises users not to publish personal information on the site - particularly Social Security numbers. Users should use a separate disposable email address and avoid giving sensitive details until the prospective employer has been established as legitimate.

The firm also recommends users to observe basic security practices, such as keeping your computer up-to-date; configuring your email to block attachments commonly used to spread viruses such as .vbs, .bat, .exe, .pif and .scr files; and of course, never execute software that doesn't come at your request, or hasn't been scanned for viruses first. ®