Premium service abusers subscribe users to various "services" that add to their phone bill at the end of the month, according to Trend Micro. This threat ranked as the highest mobile threat type, accounting for 40.58 percent of threats in 2012. A large number of the attacks are labeled as SMS Trojans, designed to send text messages to premium numbers. The premium numbers often charge a costly fee for unwanted services. Security firm F-Secure detected premium service abusers that slipped into the Google Play official Android app market masquerading as free versions of many popular applications. They were quickly removed, but not before being downloaded thousands of times.