Music and movie files could be under threat as a new trojan has come to light which alters file codes and causes Windows Media Player to access a malicious URL when the files are played – and this results in more malware being downloaded on to the compromised computer.

According to the security company's Response Blog, Symantec has observed an increase in the number of computers affected by Trojan.Brisv.A, which infects .asf, .mp2, .mp3, .wma and .wmv  movie and music files.
In a further twist to the Trojan's payload, all .mp2 and .mp3 files found on the computer are converted to the Windows Media Audio (WMA) format. This creates problems for security researchers writing software to remove the infected code from the files and restore them to their previous states.
It also makes it difficult to ascertain which files contain legitimate Digital Rights Management code and which ones have been modified by the Trojan, which makes the cleanup that much more challenging.
With people increasingly choosing to keep their music collections on their computers, often not backed up due to the size of the libraries, the impact of this threat is significant.
According to the blog, the impact of the Trojan has been further magnified by the appearance of infected movie and music files on file-sharing networks. In many cases, users will be unaware that their media files have been infected and may continue to share them – legally or illegally – causing further dissemination of the threat.