A benign barcode scanner with more than 10 million downloads from Google Play has been caught receiving an upgrade that turned it to the dark side, prompting the search-and-advertising giant to remove it.
Barcode Scanner, one of dozens of such apps available in the official Google app repository, began its life as a legitimate offering. Then, in late December, researchers with security firm Malwarebytes began receiving messages from customers complaining that ads were opening out of nowhere on their default browser.
Malwarebytes mobile malware researcher Nathan Collier was at first puzzled. None of the customers had recently installed any apps, and all the apps they had already installed came from Play, a market that despite its long history of admitting malicious apps remains safer than most third-party sites. Eventually, Collier identified the culprit as Barcode Scanner. The researcher said an update delivered in December included code that was responsible for the bombardment of ads.
“It is frightening that with one update an app can turn malicious while going under the radar of Google Play Protect,” Collier wrote. “It is baffling to me that an app developer with a popular app would turn it into malware. Was this the scheme all along, to have an app lie dormant, waiting to strike after it reaches popularity?”
Collier said that adware is often the result of third-party software development kits, which developers use to monetize apps available for free. Some SDKs, unbeknownst to developers, end up pushing the limits. As Collier was able to establish from the code itself and a digital certificate that digitally signed it, the malicious behavior was the result of changes made by the developer.
The researcher wrote:
In the case of Barcode Scanner, malicious code had been added that was not in previous versions of the app. Furthermore, the added code used heavy obfuscation to avoid detection. To verify this is from the same app developer, we confirmed it had been signed by the same digital certificate as previous clean versions. Because of its malign intent, we jumped past our original detection category of Adware straight to Trojan, with the detection of Android/Trojan.HiddenAds.AdQR.
Google removed the app after Collier notified the company. So far, however, Google has yet to use its Google Play Protect tool to remove the app from devices that had it installed. That means users will have to remove the app themselves.
Google representatives declined to say whether the Protect feature did or didn’t remove the malicious barcode scanner. Ars also emailed the developer of the app to seek comment but hasn’t received a response.
Anyone who has a barcode scanner installed on an Android device should inspect it to see whether it’s the one Collier identified. The MD5 hash digest is A922F91BAF324FA07B3C40846EBBFE30, and the package name is com.qrcodescanner.barcodescanner. The malicious barcode scanner shouldn’t be confused with the one here or other apps with the same name.
The usual advice about Android apps applies here. People should install the apps only when they provide true benefit and then only after reading user reviews and permissions required. People who haven’t used an installed app in more than six months should also strongly consider removing it. Unfortunately, in this case, following this advice would fail to have protected many Barcode Scanner users.
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It’s also not a bad idea to use a malware scanner from a reputable company. The Malwarebytes app provides app scanning for free. Running it once or twice a month is a good idea for many users.
This story originally appeared on Ars Technica.
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