No.  BUS certifies its own software is 100% virus free, and emails sent to you are automatically scanned.  The only other thing downloaded will be your own files that you retrieve from the BUS server if you require them.

Note that if you have any viruses in your own files, these will not be removed by the BUS system [since the BUS system merely encrypts and compresses your data  -  it does not scan it for viruses or other malware].