Seventeen Android Nasties Spotted in Google Play, Total Over 550K Downloads

Bitdefender researchers recently found 17 Google Play apps that, once installed, start hiding their presence on the user’s device and constantly display aggressive ads. While not malicious per se, the tactics they use to smuggle themselves into Google Play and dodge Google’s vetting system are traditionally associated with malware.

Waiting 48 hours before hiding their presence on the device, splitting the app’s code into multiple resource files, and holding off displaying ads until 4 hours after app installation are among the tactics these developers use to plant their apps onto Google Play.

With over 550,000 downloads in total, the apps found have flown below the radar of Google’s vetting system mostly because they also delivered on their promise: they do what they say they do.

At the time of writing, Google has been notified and the reported apps are being taken offline.

The Promise of Adrenaline

The description for one of the apps analyzed involves enticing users with a racing simulator that also offers in-app payments for extra in-game features.

While the gaming part works just fine, the app shows popup ads when the user is not playing the game and hides for some time following the installation. The ads are displayed at random time intervals, making it hard for users to recognize a pattern of when ads are shown.

Under the Hood

The app comes with a second component found in an archive from the assets directory. Interestingly, the malicious code resides in the first component, the second one being the actual game code. The second dex (component) and the libraries used by the game are extracted from the archive identified in the assets directory.

In terms of registered receivers, the first one is for android.intent.action.BOOT_COMPLETED. When the broadcast is received, the app will begin an activity, which starts a job scheduler for showing ads. The scheduled service starts after 10 minutes and shows an ad only once. The scheduler recreates itself by calling the method from the activity that created it initially, then starts again after 10 minutes.

Another receiver the app registers is for android.intent.action.USER_PRESENT. Whenever the user unlocks the device, if at least 4 hours have passed since the app installed it, there is a chance an ad will show. That’s because the ad displays are programmed by generating a random number of less than 3 that is checked against a value. If the number generated is equal to the check number, an ad appears. Therefore, the probability of displaying ads is once every three times the user unlocks the phone.

Adware SDKs

Users see multiple ads either in-game when pressing different buttons or even if not in the app. The frequency at which ads appear while in the game depends on a random value. In half the cases, there is a probability that when using some game functionalities, an ad pop ups.

The ad-showing mechanisms are scattered around the application, within multiple activities, and using modified adware SDKs. The randomness of ad occurrences and display time intervals is modified by the developer to decrease the likelihood of users noticing any patterns.

The adware SDK key identifiers are set in a config file within the assets directory and retrieved when showing ads. In the config file, there are parameters for customizing how often ad-displaying services should be recreated. The config file also contains a flag stating if the app should hide its presence on the device or not, a flag that is set to true by default.

Some versions of the app have the “hide icon flag” under a different name:

Fig 2. Different name for “Hide Icon” flag

Mechanisms for Dodging Google Play

One method for the app to dodge Google Play checks is by waiting 48 hours to hide. The code is also split in two dex files, making it difficult for security researchers to grasp the logic of the app. Another technique used is to manipulate the broadcast receiver for android.intent.action.USER_PRESENT to display ads only after 4 hours following installation.

The app also comes with game-related .so files that are not used. These library files are common in Android games, as they provide fast graphics rendering on a mobile environment with limited resources. What is interesting here is that the game actually uses the other .so files found in an archive within the assets directory, despite already having them in the lib directory. This could be a mechanism intended to make the app give the impression of being an average game, while its main purpose is to aggressively display ads.

Other Versions, Same Reviews

In other versions, including versions that were at some point on Google Play, requests to the ad web sites also contain sensitive information about the user, such as phone model, IMEI, IP address, MAC address, and location information. Some apps have no second dex and have all the functionality in the initial one.

Some users that have tried the apps left reviews that raised warning signs about the apps’ behavior. While some users were irked that they couldn’t even play the game because of full screen ads, other complained of battery drainage and accurately identified an app’s dubious hiding behavior after installation.

Fool me … 17 times

The methods described above to dodge Google’s vetting system seem to have been put to good use, as Bitdefender researchers have identified 17 other apps that share the same practices. While the creators’ and applications’ names are different, they all share the same features in terms of hiding their existence and displaying ads.

Stay Safe

While the Google Play apps found are not tagged as malware, but more as Riskware, users are strongly encouraged to always have a security solution installed on their devices, as it can accurately identify these apps and prevent users from installing them. Whether downloaded from official or third-party marketplaces, a mobile security solution will keep users safe from malware, riskware, or other potentially malicious apps as well as phishing or fraudulent websites.

Bitdefender identifies the found samples using the following detections: Android.Riskware.HiddenAds.HH, Android.Riskware.HiddenApp.AX, Android.Riskware.HiddenApp.HU.

All found versions:

75fd1658cd6cb56f9194dbb1aabadd64	com.walllive.wallpaperlive
577cda66d8726e4a08840c78a093c133	com.walllive.wallpaperlive
c67ec562bd0ad132eb035f36fd897333	com.walllive.wallpaperlive
64a53d16d887a49192e5bbdc3c50495a	com.ahau.qrcodeahau
30967bfb566795cce63c6ba4688953f3	com.ahau.qrcodeahau
01497636a3eb58240ded25dc13b20836	com.dailyapp.hinhnenhd
0eec8a0c529d1d28ffa098b7400da745	com.dailyapp.hinhnenhd
16075e91f122c225d19c8b9e4abe5e90	com.king.qrcode.barcode.uk
ffea0e7167b7426422e1bdb8053b338e	com.calendar.ovulation.timer
14eb19b71b708be916ac5981fdb3478e	com.dailyapp.hinhnenhd
65db221140f32f43514a7449abdea74a	com.king.qrcode.barcode.uk
133f0f7726f067adc163558ffc211a57	com.sdcard.filemanagernham
fbea116dc453f460dcdbe8658f6904bf	com.sdcard.filemanagernham
6935df9ea6334e478a5fdc0dc54b2f5e	com.king.qrcode.barcode.uk
94825120ab63ea35051e0c6215e57292	com.livewapper.livewappernham
9f12a4b92280e73a8019ad0fcd0767ad	com.calendar.ovulation.timer
0ce8f2d5429bf41992b08521faf00aa4	com.livewapper.livewappernham
3d6cca1675db1e518694aff939f2eb9e	com.livewapper.livewappernham
c91da7fb949f2665ca6a5ef56f881da6	com.dailyapp.hinhnenhd
2f87caa40516e5c51444f31363349900	com.tingrdoumanh.xily
04c9865ba8a7f9e2ebeb3dde4abeb8aa	com.sdcard.filemanagernham
afdd1ec96fc2cc7e1f9e581143b6390f	com.king.qrcode.barcode.uk
6f2017bf31b5557d9dbbc4b343beb4f0	com.stream.streammorriorthien
1f67cdc2c32754975e4d010198685a69	com.smartfile.smartfilemobile
496fc51fd0e08a46bc2bc304c0398175	com.sdcard.filemanagernham
b0c09bc35c47e55fd425f307ff978aa4	com.king.qrcode.barcode.uk
3430c8ebb5fe9b07bc6f53d85718f937	com.dailyapp.hinhnenhd
d027a7c9b1d9f48466cc444b241d5040	com.racing.car3dnham
13f656fbc27570a19f81472bf77c1af6	com.smartmobile.tranferfilesmart
01fa5e94133bd0add8132dfca451d0b7	com.stream.streammorriorthien
b3d9e60e27bf563e161fb37b0a4f291e	com.weather.weatherapppirlo
8a13765c04cd2127af90078e2f7488c1	com.racing.car3dnham
e5879256315957b2a77e23facea6b0aa	com.stream.streammorriorthien
4c9507a2635085516d5cc01245762650	com.dailyapp.hinhnenhd
4919d022e76c825fde52973401a7e5f4	com.livewapper.livewappernham
5d7039c91782c3b13f9ad9ebb8198dac	com.calendar.ovulation.timer
cb79eaabfd18429c76db8c9786773cfe	com.king.qrcode.barcode.uk
e0e9f7aff0ed38406c50dd6b97d78c2c	com.livewapper.livewappernham
d37baf314d582e6a5a7cb8f57d01e013	com.sdcard.filemanagernham
dcdfcbdcc71333b0f89262c6b1b5cb70	com.ahau.qrcodeahau
d087bab15572425fcabccc131a1d1b35	com.tingrdoumanh.xily
419141d15e3a152147c954054b9a3d19	com.stream.streammorriorthien
5aefbb39e60c722ede71ed3829bef1b1	com.lives.wallpapperathien
b7403793bccb634aeefa548db903d35c	com.weather.weatherapppirlo
ccdfe80d95b1442e64d3094f89a538f9	com.ahau.qrcodeahau
55437c0261d683294b491f2c1b6cb6ba	com.dailyapp.hinhnenhd
b5880a1f5dfee2039ff303aa765f4560	com.king.qrcode.barcode.uk
40136fbc34306c0ffc1dd55e35bb5819	com.livewapper.livewappernham
9c6f75ea9cdf7dbf7ff59c721f10a5eb	com.calendar.ovulation.timer
7df3cfd784a7ab16152685d0a18f7b9c	com.sdcard.filemanagernham
dd847c8f65a347dd959fac326f4a9f36	com.stream.streammorriorthien
2789b7dff80967214264db7f8806b1fe	com.at2.qrcodereaderat2020
1698c88584ff5f76d8b8551c6d43fb54	com.at2.filemanagerat2020
82cd92b011dff773c886206baba0f6ec	com.at2.wallpapperat2020
8bb95db44055d508e341eb7f8bf296a2	com.ahau.qrcodeahau
0e3ae8d6680198351e61aa1c0b71fe98	com.funkd.salondoctor
e46ff27ead1f32954268e7fed6bb24aa	com.emerency.vanlopegames
5fa880af82079cab1245e2fd361919ad	com.dailyapp.hinhnenhd
e3fe1a6b45625bdb27ad6b8dd14609f5	com.sdcard.filemanagernham
8f8b90cd8e9e9a59bc905aed996c24bf	com.checkup.mommygames
038d1f647f211cf5aad2485b1cbf68df	com.livewapper.livewappernham
6a8e937ef3309d4408aa4fca60bf418e	com.at2.filemanagerat2020
209ef095a9a21547709ec78811b3b6d9	com.checkup.mommygames
9429361d98ba9a59e30f50fa4295eed0	com.king.qrcode.barcode.uk
7d8262f651e4d8891128e03263f917fe	com.calendar.ovulation.timer
59fcde6b9b629e30bc9ee6659785a357	com.smartapp.vpnat2020
afaaf9b96bace39efd792c96853a7a79	com.at2.wallpapperat2020
18d408f40ed312fdc6284381ce0ba93b	com.at2.qrcodereaderat2020
379ae1aea09824c4ec4d133e485339b1	com.at2.filemanagerat2020
3a9d03500bbb615d1ab63f03c1e6fff0	com.at2.qrcodereaderat2020
a4bdd75c306838b164f853cc5a6eee94	com.alerflash.missmobies
292ba0ee434e472ba3e11ac941da4411	com.stream.streammorriorthien
9eb2e6837bd071a6611180c9bc4a7998	com.ahau.qrcodeahau
982c61b96f6405521fe3e56c6854f4f9	com.smartmobile.tranferfilesmart
5f1274aa5f8a5ca3e74533b773cf31b9	com.dailyapp.hinhnenhd
b9d2227bc0d74179124191be89cb7a17	com.wallledclock.digitalapps
0c6dff9890421dfbc2f1ec0228622518	com.legendapp.qrcode20
c6174f804b2c0a79ae6aecef2d28b53f	com.livewapper.livewappernham
12c8bd527d30e42cbec2c5acc81d05f9	com.bigfish.clcbgames
1861ccc9a159675ae53c90981a80aad2	com.emerency.vanlopegames
8f6d45293d1b87d06d3039fd4a4278ae	com.bigfish.clcbgames
9eda1388d7a584e3107d9866a82df35c	com.king.qrcode.barcode.uk
cc25a0fd2bb2f10a56de321ee9aebf64	com.calendar.ovulation.timer
a0af52f538eb33cc4a36047f9b383362	com.sdcard.filemanagernham
238d799c8ac62a71199126dfcf04bdd9	com.legendapp.qrcode20
05e95ebc99ed9db1cbe2ee01051569a6	com.stream.streammorriorthien
ee716886b9a3fe201825265d0e60e91c	com.tonyfarm.smartviewfb
f9ff0977b4cc0c5c5785e3585630fbfc	com.stream.streammorriorthien
681be70820a64b1cf7b6cde2f5c5e809	com.sdcard.filemanagernham
5a38693cd123e036aee51ad4ed133783	com.at2.qrcodereaderat2020
1250f1296c0e92112d554960d4f99710	com.legendapp.qrcode20
2e11dd08a83cfb8c86372581eddf188c	com.bigfish.clcbgames
80abde70e5f4d4dc7ace31586097e026	com.legendapp.qrcode20
e739c7e31ab68a894862c751ddf9215f	com.at2.wallpapperat2020
154ac305937943be5971a938c8f5762b	com.carracing3d.newcard
e85682656b447164eba3e00c7be65a5d	com.carracing3d.newcard