An uptick in malware that infects music files being traded on popular peer-to-peer (P2P) file-sharing networks should give Windows users pause about downloading songs from unknown sources. Symantec is reporting a spike in the number of audio files infected with what it calls Trojan.Brisv.A (detected as Worm.Win32.GetCodec.a by other antivirus vendors). The malicious software resides in otherwise innocuous-looking music Windows Media Audio (.wma) files that, when opened, changes all .mp3 and .mp3 files on a host system to Windows Media Audio (.wma) format. Audio files altered by the Trojan won’t lose their .mp2 or .mp3 file extensions. Rather, the Trojan embeds in each converted media file a placeholder, so that when a victim tries to listen to it, the song is opened up in Windows Media Player. At that point, the victim is prompted to download an audio codec in order to continue playback. If the victim installs the codec,