Some Android apps thought to be vulnerable to the Heartbleed bug were spared because of a common coding error in the way they implemented their own native OpenSSL library.

FireEye scanned 54,000 Android applications in Google's Play store on April 10 to see which ones are vulnerable to Heartbleed. The flaw, publicly disclosed on April 7, is contained in OpenSSL, a code library used to encrypt data traffic.

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The security company found several games and office-based mobile applications that are vulnerable to the bug, mostly because the applications use their own native OpenSSL library rather than the one in the Android OS. Google said Android was mostly immune to Heartbleed.

"We have notified some of the app developers," wrote researchers Yulong Zhang, Hui Xue and Tao Wei on FireEye's blog.

The Heartbleed flaw is buffer overflow vulnerability in which a server returns too much information, divulging user credentials and sensitive data such as the private key for an SSL certificate.

But it can also be used to attack applications. FireEye said attacking a game could yield its OAuth token, an authentication token, which could be used to hijack an account or linked social networking accounts.

At first glance, some Android office productivity applications also appeared to be vulnerable. But the researchers found a common coding mistake actually meant the Heartbleed bug wouldn't work.

"A deeper look shows that these apps either make a mistake in the native code linkage or just contain dead code," wrote the FireEye researchers.

"Therefore, when they try to invoke SSL functions, they directly use the non-vulnerable OpenSSL library contained within the Android OS, instead of using the vulnerable library provided by the app."

FireEye also found upwards of 17 applications on Google Play claiming to detect the Heartbleed vulnerability. Only six scanned applications on an Android device. Of those six, two missed applications confirmed as vulnerable.

Others in the batch of 17 performed questionable scans and appeared to be designed to deliver advertising software.

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