This is what you get lately when you download movies, mostly via BitTorrent.

From wikipedia: 3wPlayer is a rogue media player software application bundled with trojans that can infect computers running Microsoft Windows. It is designed to exploit users who download video files, instructing them to download and install the program in order to view the video. The 3wPlayer is infected with Trojan.Win32.Obfuscated.en according to Kaspersky Anti-virus.

The 3wPlayer employs a form of social engineering to infect computers. Seemingly desirable video files, such as recent movies, are released via BitTorrent or other distribution channels. These files resemble conventional AVI files, but are engineered to display a message when played on most media player programs, instructing the user to visit the 3wPlayer website and download the software to view the video. The program is bundled with malware that has various undesirable effects, including attempting to disable the user's anti-virus software.

There are several tools on the internet that claim to be able to decode these media files, but are generally second-chance attempts at infecting your computer with malware. To date, these programs have not been proven to work, and it is believed that any downloaded file that requires the 3wPlayer will not contain any of the promised content.