Enlarge / A cryptocurrency mining farm. (credit: Marco Krohn)

The Internet is awash with covert crypto currency miners that bog down computers and even smartphones with computationally intensive math problems called by hacked or ethically questionable sites.

The latest examples came on Monday with the revelation from antivirus provider Trend Micro that at least two Android apps with as many as 50,000 downloads from Google Play were recently caught putting crypto miners inside a hidden browser window. The miners caused phones running the apps to run JavaScript hosted on Coinhive.com, a site that harnesses the CPUs of millions of PCs to mine the Monero crypto currency. In turn, Coinhive gives participating sites a tiny cut of the relatively small proceeds. Google has since removed the apps, which were known as Recitiamo Santo Rosario Free and SafetyNet Wireless App.

Last week, researchers from security firm Sucuri warned that at least 500 websites running the WordPress content management system alone had been hacked to run the Coinhive mining scripts. Sucuri said other Web platforms—including Magento, Joomla, and Drupal—are also being hacked in large numbers to run the Coinhive programming interface.