Beware ad slingers thinly disguised as security apps

According to AV-Comparatives, an independent testing organization, there are significant differences in the level of protection provided by mobile security solutions. However, even the poorest of them are still far better than questionable apps that impersonate security applications in order to display ads to users. Thirty-five such applications have recently been discovered in the Google Play official Android app store.

These apps have flown under the radar for a few years, with Google Play statistics showing a minimum of over six million installs, cumulatively. However, not all those were necessarily real installations: it’s a common practice to make fake downloads by bots that subsequently post positive reviews and improve their respective app’s ratings.

All 35 apps have been flagged by ESET and eventually removed from the store.

Figure 1 – The 35 apps in question on Google Play

On top of annoying their victims with ads, disguising these apps as security software has some serious negative side effects, too. In mimicking basic security functions – in fact, they all act as very primitive security checkers relying on a few trivial hardcoded rules – they often detect legitimate apps as malicious. And last but not least, they create a false sense of security in the victims, which might expose them to real risks from malicious apps that are not detected as such.

ESET’s analysis has shown that among these 35 apps, only a handful stand out for their specific features: one app is not completely free as it offers a paid upgrade; one app has implemented a primitive, easily bypassed, app-locker manager; another app flags other apps from this group as dangerous by default; and finally, one misuses ESET’s branding.

Figure 2 – One of the 35 apps detecting other, similar apps as ‘High Risk’

Figure 3 – One of the apps flagging itself as ‘High Risk’

Figure 4 – One of the apps offering a ‘Pro plan’

Security-mimicking functionality

In order to stay under the radar, all the shady ad-displaying apps mimic actual mobile security solutions. However, their ‘detection mechanisms’ are incomplete and very primitive, which makes them easy to bypass and prone to false positives.

Our research into these questionable apps has shown that their ‘detection mechanisms’ can be divided into four categories. These mechanisms are identical or almost identical across the whole set of apps.

1) Package name whitelist & blacklist

These whitelists features popular apps such as Facebook, Instagram, LinkedIn, Skype and others. The ‘blacklists’ contains far too few items to be considered security functionality at all.

Figure 5 – Whitelisting popular apps

2) Permissions blacklist

All apps (including legitimate ones) are flagged if they require some of the listed permissions that are considered dangerous, such as send and receive SMS, access location data, access the camera, etc.

Figure 6 – Permissions blacklist

3) Source whitelist

All apps but those from the official Android store, Google Play, are flagged – even if they are completely benign.

4) Activities blacklist

All apps that contain any of the blacklisted activities: that is, parts of applications. This mainly concerns some ad-displaying activities.

Flagged are all apps that contain any of the blacklisted activities, i.e., packages of application that are used in an application. These packages can handle additional functionalities (mainly some ad-displaying activities).

While there is nothing wrong with the idea of activity blacklisting, the implementation in these questionable apps is rather sloppy. For example, Google Ads is included in the blacklist despite the fact that it is a legitimate service. On top of being legitimate, this service is implemented in all of the shady apps we analyzed.

Figure 7 – Activity blacklist

Additional security “functionality”

Some of the questionable security apps are capable of protecting a user’s apps with a password or a pattern locker. The idea behind this seemingly useful feature is to provide the user with another layer of security in selected apps.

However, due to insecure implementation, this feature also fails to provide true security to the user.

The problem is that relevant information is not stored safely on the device – instead of using encryption, which is common baseline practice in cybersecurity, these apps store the names of locked apps and the passwords to unlock them as plaintext.

This means that the data can be accessed after the device is rooted.

Besides compromising the unencrypted data by rooting the phone, there is another way to bypass the app lock. An attacker with physical access to the device can change the app-locking password without knowing the old one!

Figure 8 – One of the questionable apps with app locking functionality storing user data in plaintext

Conclusion

 Having a security solution installed in an Android phone is definitely a good thing. However, not all apps featuring “security” or “antivirus” in their name do what the name promises. Before installing a security solution, think twice: is it really a tool you can safely rely on?

The 35 pseudo-security apps described in this article are not, say, ransomware or other hardcore malware. The only harm they do is displaying annoying ads, making false-positive detections and giving the victim a false sense of security. However, those millions of unwary users who downloaded them could easily have ended up downloading true malware in some similar disguise.

Instead of shady apps with flashy names and icons and outlandish, unsubstantiated promises, seek a reputable security solution. And which one to choose? An independent test by a well-respected testing organization might help.

IoCs

ESET detection name:

Android/Blacklister.A application potentially unwanted