Trojans are malicious applications that pose themselves as legitimate software in order to trick users to install them. Once on the victim's machine, it may run any number of malicious process to steal vital information or inflict damage to other software.
Trojan.Media-Codec is a downloader trojan that often drops more threats into an infected computer and executes them. This trojan typically uses deceptive tactics, like pretending to be a codec for Windows Media Player in order for the user to install it. Spotted on adult material sites, but also spotted using advanced search engine spamming.
Drops rogue anti-spywares.
A License Agreement is shown during the installation process which states that:
Licensor may change homepage on user's computer and may offer additional components through our version of checking/update system. These components include: toolbar, popup ads manager, advertisements messenger, pc protection software, shortcuts manager.