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Almost every Android phone has a big, gaping security weakness, according to the security startup who discovered the vulnerability. Essentially, according to BlueBox, almost every Android phone made in the past four years (or, since Android "Donut," version 1.6) is just a few steps away from becoming a virtual George Romero film, thanks to a weakness that can "turn any legitimate application into a malicious Trojan."

While news of a security vulnerability in Android might not exactly be surprising to users, the scope of the vulnerability does give one pause: "99 percent" of Android mobiles, or just under 900 million phones, are potentially vulnerable, according to the company. All hackers have to do to get in is modify an existing, legitimate app, which they're apparently able to do without breaking the application's security signature. Then, distribute the app and convince users to install it.

Google, who hasn't commented on the vulnerability yet, has known about the weakness since February, and they've already patched the Samsung Galaxy S4, according to CIO. And they've also made it impossible for the malicious apps to to install through Google Play. But the evil apps could still get onto a device via email, a third-party store, or basically any website. Here's the worst-case scenario for exploitation of the vulnerability, or what could potentially happen to an infected phone accessed via an application developed by a device manufacturer, which generally come with elevated access, according to BlueBox:

Installation of a Trojan application from the device manufacturer can grant the application full access to Android system and all applications (and their data) currently installed. The application then not only has the ability to read arbitrary application data on the device (email, SMS messages, documents, etc.), retrieve all stored account & service passwords, it can essentially take over the normal functioning of the phone and control any function thereof (make arbitrary phone calls, send arbitrary SMS messages, turn on the camera, and record calls). Finally, and most unsettling, is the potential for a hacker to take advantage of the always-on, always-connected, and always-moving (therefore hard-to-detect) nature of these “zombie” mobile devices to create a botnet.

The company recommends users of basically every Android phone double check the source of any apps they install, keep their devices updated, and take their own precautions to protect their data. But as TechCrunch notes, Android users really should be doing this anyway, as the devices tend to come with a " general low-level risk" from malware. That risk, however, is elevated for users who venture outside of the Google Play store for their apps.

So while the actual impact of the vulnerability is not known, neither is the timeline for fixing it. Manufacturers will have to release their own patches for the problem in order to fix it, something that happens notoriously slowly among Android devices.

This article is from the archive of our partner The Wire.