Hackers are targeting companies looking to recruit staff through Monster Jobs using the Gameover Zeus malware, according to security firm F-Secure.
F-Secure researchers reported the campaign in a blog post. F-Secure security analyst Sean Sullivan told V3 the campaign uses a two-stage strategy to take control of the accounts. The first stage sees the hackers infect the victim's system with the Gameover malware.
"Gameover Zeus gets installed in the usual fashion from bait of some sort: spam or malvertising, exploit kit, bot installer. Once installed Gameover is able to grab information from forms – so the username and passwords as they are typed," explained Sullivan.
In the second stage of the attack, the hackers attempt to dupe the users to hand over the remaining information needed to fully take control of the account using a bogus security check form, said Sullivan.
F-Secure said the purpose of the attack remains unknown, though it is likely designed to target the accounts of HR departments using Monster.
"HR recruiters with website accounts should be wary of any such irregularities. If the account is potentially tied to a bank account and a spending budget, it's a target for banking Trojans," read the post.
At the time of publishing Monster had not responded to V3's request for comment on the Gameover campaign.
Sullivan told V3 the nature of the malware means it is currently unclear how many victims the Gameover campaign has ensnared. "It's a peer-to-peer botnet so it's tricky to count," he said.
But Sullivan added: "There is some excellent analysis from Dell SecureWorks, which details about 24,000 Gameover bots, in July 2012. I haven't seen any attempts to count the entire Gameover botnet recently, but I'm sure it's still in the multiple tens of thousands."
F-Secure said the campaign could easily be dealt with if Monster adopted a more robust account authentication system. "It wouldn't be a bad idea for sites such as Monster to introduce two-factor authentication, beyond mere security questions," read the post.
Two-factor authentication is an increasingly common security protocol for online service providers. Numerous companies including Tumblr, Twitter and Dropbox have added the feature to their respective services over the past two years.