The program trojan.medfos belongs to the Win32/Medfos family of Trojan downloaders that installs on the PC through distribution channels like peer-to-peer (P2P) networks, the Internet Relay Chat (IRC), and spam email. It downloads malware from malicious sites by hijacking the Web browser and redirecting searches to sites that host exploits and other security threats, including advertising websites that employ pay-per-click techniques. It also downloads and installs arbitrary files to the PC when commanded by its author.