Cheap Android TV boxes have quietly become one of the most dangerous devices on the home network, not because of what you watch on them but because of what they might be doing in the background.

Researchers still don’t know the cause of a recently discovered malware infection affecting almost 1.3 million streaming devices running an open source version of Android in almost 200 countries.

On the surface, the Superbox media streaming devices for sale at retailers like BestBuy and Walmart may seem like a steal: They offer unlimited access to more than 2,200 pay-per-view and streaming ...