Recent visitors to Plenty of Fish (pof.com), an online dating website with over 3 million daily active users, had their browsers redirected to exploits that installed malware.
The attack was launched through a malicious advertisement that was distributed through a third-party ad network, researchers from security firm Malwarebytes said in a blog post Thursday.
The malicious ad pointed to the Nuclear exploit kit, a Web-based attack tool that exploits known vulnerabilities in browsers and popular browser plug-ins like Flash Player, Java, Adobe Reader and Silverlight.
If the attack is successful, the tool installs malware programs on users' computers. The Malwarebytes researchers haven't captured the payload from the Plenty of Fish attack, but a malvertising campaign launched through the same ad server a day earlier distributed an online banking Trojan program known as Tinba.
"Given that the time frame of both attacks and that the ad network involved is the same, chances are high that pof[dot]com dropped that Trojan as well," the researchers said.
The server that distributed the malicious ad is ad.360yield.com and appears to be operated by a real-time advertising firm called Improve Digital that's headquartered in Amsterdam. The company did not immediately respond to a request for comment.
This attack does not mean that Plenty of Fish had its servers or systems compromised, like what recently happened to adult dating site Ashley Madison.
Malvertising attacks are the result of criminals tricking or hacking into advertising networks so they can display malicious ads on legitimate websites that use those networks.
This kind of attacks have been around for years, despite significant efforts by advertising companies to prevent them, and are quite dangerous because they are completely transparent to the victims. Users just browse to a known and trusted website and have their computers infected in the background.
Since exploit kits like Nuclear typically target known vulnerabilities, it's important to keep software programs, especially browser plug-ins, up to date. Running up-to-date antivirus products that could detect the exploit payload, even if the exploit is successful, is also very important.
Even if you've taken all these precautions, if you visited pof.com recently it's probably best to run a malware scan as soon as possible.