More than 130 Android apps on the Google Play store have been found to contain malicious coding, possibly because the developers were using infected computers, according to security researchers.
The 132 apps were found generating hidden iframes, or an HTML document embedded inside a webpage, linking to two domains that have hosted malware, according to security firm Palo Alto Networks.
Google has already removed the apps from its Play store. But what's interesting is the developers behind the apps probably aren't to blame for including the malicious code, Palo Alto Networks said in a Wednesday blog post.
Instead, the platforms the developers used to build these apps were probably infected with malware that looks for HTML pages and then injects the malicious coding, the company said.
Many of these tainted apps offered design ideas for things like cheesecakes, landscaping a garden, or laying out a patio. The most popular had more than 10,000 downloads.
When installed, the apps would display seemingly benign webpages. However, in reality, the pages shown contain a tiny hidden iframe that links to two suspicious domains.
Both domains were previously involved in hosting Windows malware. But in 2013, a Polish security team took over the domains, and they've effectively been shut down, Palo Alto Networks said. Nevertheless, Google still flags them as dangerous to visit.
Why the apps were linking to two malicious, but defunct domains still isn't clear. However, Palo Alto Networks also came across one peculiar app sample that didn't contain the problematic iframes, but instead a Microsoft Visual Basic script used for Windows.
It's an odd thing to include, given that the script won't harm any Android users. But it's possible the developers behind these apps had their Windows machines infected with malware.
Some malware, such as the Window-based Ramnit, have been known to search for files on a computer and inject them with malicious coding, Palo Alto Networks said. "After infecting a Windows host, these viruses search the hard drive for HTML files and append iFrames to each document," the company said.
"If a developer was infected with one of these viruses, their app's HTML files could be infected," Palo Alto Networks added.
In another scenario, it's possible the app makers downloaded developer tools that were already tainted with the malicious coding.
Because these 132 apps linked to two now defunct malicious domains, they actually don't pose much of a threat. It may be that whoever tampered with these apps did so accidentally.
"File infecting viruses can bounce around for years, even after these domains are taken offline," Ryan Olson, intelligence director at Palo Alto Networks, said in an email.
"They also typically infect executable files and copy themselves to USB and shared drives," he added. "The malware that wrote the iframe to these files was probably released before the domains were sinkholed."
Still, the bigger worry is that someone else might try to replicate the attack to cause actual danger, like secretly infecting developer apps to steal users' information or drop other strains of malware.
"It's easy to envision a more focused and successful attack," Palo Alto Networks said in its blog post.
The developers of the 132 apps come from seven different parties, but appear to all have ties with Indonesia, the security firm said.