Unfortunately MSN is a way in for all types of virus to your PC. This means that an antivirus created specifically to detect the possible external threats that enter via MSN exists: MSN Virus Remover (also known as MSN Virus Removal).
MSN Virus Remover is applicable both to MSN and to Windows Live Messenger, checking, detecting and analyzing your MSN continually to assure you that no known virus can enter (the database has thousands).
MSN Virus Remover also comes equipped with its own Windows Registry editor, and even lets you restore the system returning it to a previous version that you had before it was infected by a virus.
VTE Virus Scanner 2.0.0.3 ( 2008-02-23 ) Impressive and efficient free antivirus of high quality that detects and destroys trojans, viruses, spyware, etc.