Merr.com has virus protection software on its mail server, which scans all incoming e-mail looking for known viruses. If it detects a virus in the email, it deletes the email.  

Since viruses change constantly, we recommend that our customers also install and maintain virus software on their own machines to detect new viruses that may be missed by the virus protection software on the mail server. We recommend Norton AntiVirus or McAfee VirusScan.

A free online virus scan service is offered by Trend Micro.