We heard that the latest avast! Anti-Virus reports that one file in our installer (belc.dll) is infected by a Trojan Horse (Win32:Agent-AKK [Trj]). Fortunately we can assure you that this is not the case, all our publications are 100% checked for any malicious code before we distribute it. This is just one of those famous "false positives", avast! has to update their code/definitions, there's nothing we can do about it.
Other than being very seductive MP won't harm you or your HTPC.
So as long as you download MediaPortal installers, plugins, whatever from THIS website (rather than any other ways of distribution, Torrent or other networks/servers/websites), we can guarantee everything is and will be clean. Only SourceForge and Download.com are officially mirroring our installers. Also all uploads in our repository get checked before being published. 

Update: The latest definitions do not have this problem anymore.