Bitcoin and other cryptocurrencies have been making waves over the last few years based on their growth and impact on markets around the world. However, its popularity has resulted in savvy developers creating applications for Android devices that mine currency at the expense of users CPU.

Cryptomining techniques have been hiding in the background of some apps in the Google Play Store with about 15 million user downloads of such applications. They can cause battery life and performance issues because they eat up the CPU cycles of the device to generate revenue for the developer.

Ars Technica reported two applications were discovered to have been downloaded over 50,000 times where Bitcoin mining is being performed behind the scenes inside hidden browser windows. Presently, at least four apps are using the same technique (some without user permission) and have been downloaded well over one million times.

Some apps have eliminated the feature while other apps have encouraged people to permit the practice. One application informed users that when their device was idle, it would use the CPU to generate coins. This default option was able to be turned off by the user, however.

Android cryptocurrency mining malware can be very profitable for developers. While the maliciousness of these types of methods embedded inside applications can vary, it's clear that a new method of monetization is emerging. Millions of users are, unknowingly in most cases, actively mining for a developer's personal profit.

According to Ixia, sometimes a user is prompted to update the application and once downloaded, the mining "feature" is then pushed to the device. As mobile devices continue to evolve and gain more and more processing capabilities in the form of CPU cores and RAM, smartphones and tablets will be increasingly lucrative targets for stealth cryptomining. Be sure to exercise caution and read what permissions you're granting to applications, before installing them on your device.

Should Google impose restrictions on these types of apps appearing in the Google Play Store? Drop a comment below and let us know what you think.