Researchers at Russian anti-virus company Doctor Web recently uncovered three malicious Android apps on Google Play that install the Android.SmsSend Trojan, which sends text messages to premium numbers without the user's permission.

All three apps, which are audio players and a video player that displays adult content, were uploaded by a Vietnamese developer called AppStore Jsc.

According to Doctor Web, the apps have been installed between 11,000 and 25,000 times.

Each app asks the user for permission to download additional content, such as adult video clips in the case of the video app -- but that download the installs the Trojan.

"The program covertly sends short messages to the short number 8775 which is specified in the malware's configuration file," Doctor Web notes. "It is noteworthy that this Trojan really does enable a user to view adult video clips. Apparently, the attackers implemented this feature to avoid unnecessary suspicion."