Another WhatsApp modification, known as YoWhatsApp, has turned out to be malicious: it downloads the Triada Trojan to smartphones, which shows ads, secretly subscribes the user to paid content, and steals WhatsApp accounts. How did this happen and what lessons can we learn?

Don’t feed crocodiles with your hand, or Simple Cybersecurity Rules

Probably the most important rule of information security is to reduce your risks. To do this:

• Don’t visit suspicious websites — they may contain malicious ads or be a front for a phishing scam.
• Don’t download hacked versions of programs via torrents. If you do, there’s a good chance that cracks will contain a password-stealing Trojan, for example.
• Don’t click on links in e-mails that were sent from unknown addresses, and don’t open attachments — there could be all kinds of malware lurking there.

You get the idea: being careful goes a long way toward protecting yourself against cyberthreats.

At the same time, it’s still important to keep your antivirus enabled and updated — as insurance in case something happens. Don’t tempt fate by doing the online equivalent of walking down a deserted alley late at night. If you apply a little bit of common sense, you can greatly reduce your chances of falling prey to scammers.

In addition to the above-listed ways to lower the risk of something bad happening, it’s worth adding one more: don’t download mobile apps from unofficial sources. Google and Apple verify apps before adding them to their stores, so the chances of encountering malware there are slim — albeit still not zero (especially in the case of Google Play). Huawei does the same with its Huawei AppGallery store, although malware has already been found there too. But it’s much more likely that you’ll run into malware on open platforms that let you simply download an APK file.

There’s another key security rule: don’t use unofficial clients for messaging apps. To understand why this is important, let’s take a few steps back and look a little more closely at how messaging apps work.

Most of them operate according to the client-server model, where the user interacts directly with the client app. Data exchange between client and server occurs through a special protocol. For many messaging apps this protocol is open. This makes it possible to create unofficial modified clients with additional features, such as viewing messages other users have deleted, creating mass mailings, customizing the interface, and so on.

So where’s the danger? With official clients, you’re entrusting your correspondence only to the creator of the messaging app. When you use an unofficial client, you’re entrusting it not only to the developers of the messaging system but also to the developers of the unofficial client app. On top of that, the modified client may be distributed through unofficial sources (which, as we recall, shouldn’t be trusted). All these are additional stages where something can go wrong — in other words, there are extra risks.

What’s up, Triada

Naturally, something did go wrong, repeating the scenario we wrote about last year. To recap: back then, attackers infected the FMWhatsapp mod with a dropper that downloaded a multifunctional Trojan — Triada — onto users’ devices. This modular Trojan mainly shows ads and signs the user up for paid content.

Now, practically the same thing has happened — with the same messaging app but a different unofficial client. This time, the YoWhatsApp mod, also known as YoWA, has been infected. This mod attracts users with expanded privacy options, the ability to transfer files up of to 700 MB, increased speed, and so on.

Apparently YoWhatsApp caught the eye of the malware distributors because it has a significant user base. Also, the fact that the mod wasn’t allowed on Google Play played into the hands of the criminals. Therefore, users are accustomed to downloading YoWhatsApp from sources of varying degrees of trustworthiness. One of the main distribution channels for the infected version of the mod was advertising in SnapTube, an app for downloading video and audio. SnapTube owners themselves probably didn’t even suspect that one of its advertising campaigns was spreading malware.

Along with the infected YoWhatsApp, users got a dropper that delivered the Triada Trojan to their device. Unlike last year’s campaign, this time the dropper wasn’t the only thing that came with the Trojan. An additional feature was added to YoWhatsApp that allow intruders to steal the keys required for WhatsApp to operate. These keys are enough to hijack an account and use it to do things like distributing malware or extracting money from the victim’s contacts.

As a result, the user not only loses money — since Triada signs them up for paid subscriptions — but also risks compromising their contacts, to whom the criminals may try to write in the user’s name.

How to protect yourself from malware on Android

The best way to fight malware is to avoid situations where you might get it in the first place. In this case, there are three simple rules to follow to protect yourself:

• Don’t download apps from unknown sources. In fact, it’s a good idea to block the ability to install apps from places other than Google Play on your Android smartphone.
• Don’t install alternative clients for messaging apps. Even if official versions of apps aren’t always ideal, they’re much more reliable and secure.
• Use good protection and always keep it enabled. Kaspersky for Android can detect different modifications of the Triada Trojan and other Android malware and block them before they have a chance to wreak havoc. Keep in mind that with the free version of our mobile protection you need to manually run the scan every time you download or install something new. The full version automatically scans every new app.