FMWhatsApp mod for WhatsApp downloads Trojans

One version of popular WhatsApp mod FMWhatsApp uses an infected advertising module that downloads Trojans to smartphones.

Popular WhatsApp mod FMWhatsApp downloads viruses that steal accounts, sign up for paid subscriptions, and display full-screen ads

We recently discovered that a version of popular WhatsApp mod FMWhatsApp includes an embedded Trojan. The Trojan, called Triada, downloads other malware to users’ devices. Here’s how it happened and why using modified versions of WhatsApp is dangerous.

Why use WhatsApp mods?

Not all users are happy with the official WhatsApp app. Some may feel a need for self-destructing messages or, conversely, the ability to view messages another user deleted. Others are after dynamic themes, and still others want to hide certain chats from the general list or automatically translate messages.

Naturally, they want these features right away, not when WhatsApp’s developers finally get around to implementing them. As a result, some users turn to the modified WhatsApp clients available online, which are fairly numerous and not hard to find.

Fans of mods are not deterred even by WhatsApp’s occasional crackdown on such modifications or the threat of account bans.

The creators of WhatsApp mods often embed ads in them — understandably — along with the features users are looking for. Problems arise, however, from their use of third-party ad modules through which malicious code can sneak in under developers’ radar.

Triada et al. in the FMWhatsApp mod

That’s precisely what happened with FMWhatsApp, a popular WhatsApp mod. In version 16.80.0 the developers use third-party ad module that includes a Trojan. Our mobile antivirus solution detects this malware as Trojan.AndroidOS.Triada.ef.

We saw a similar situation in the spring of 2021 with the APKPure unofficial app store, whose developers also used an ad module from an unverified source, thereby infecting their creation, and consequently users, with the Triada Trojan (albeit a slightly different version).

As in the case of the infected APKPure, the Triada Trojan in the dangerous version of the FMWhatsApp mod performs an intermediary function. First, it collects data about the user’s device, and then, depending on the information, it downloads another Trojan.

Triada’s “extras” come in a variety of flavors — the infected version of FMWhatsApp downloads several types of malware to devices:

  • Trojan-Downloader.AndroidOS.Agent.ic, a Trojan that downloads and runs other malicious modules;
  • Trojan-Downloader.AndroidOS.Gapac.e, which downloads and runs other malicious modules and can also display full-screen ads at unexpected moments;
  • Trojan-Downloader.AndroidOS.Helper.a, which downloads and runs the installer module of the xHelper Trojan and runs invisible ads in the background;
  • Trojan.AndroidOS.MobOk.i, a Trojan that signs up for paid subscriptions;
  • Trojan.AndroidOS.Subscriber.l, another Trojan that signs up for paid subscriptions;
  • Trojan.AndroidOS.Whatreg.b, the most complex Trojan in the list, signs in to the WhatsApp account on the victim’s phone, intercepting the login confirmation text. The device can then become a site for various types of illegal activity such as spam distribution or illegal trading.

Our Securelist post delves more into the FMWhatsapp mod’s Triada Trojan.

How to defend against such attacks

Practicing caution and using your device safely is key to keeping malware and other mobile nasties off your phone. Generally speaking, follow these tips to avoid trouble:

  • Avoid installing apps from unofficial sources and use your device’s settings to deny permission to install them. (If you need to install an app not from an official store, temporarily enable that permission and then disable it again);
  • Use only official messaging apps, and download them only from official app stores — they may lack some features, but will not flood your phone with viruses;
  • Check what permissions you’ve granted to installed apps — some might pose a real threat;
  • Install a reliable mobile antivirus app on your phone, and heed its warnings.