Malware is software designed to infiltrate or damage a computer system without the owner's informed consent. It is a portmanteau of the words "malicious" and
"software". The expression is a general term used by computer professionals to mean a variety of forms of hostile, intrusive, or annoying software or program code.
Setting up a malware blacklist in Postix MTA is quite easy. The Malware Block List is a free, automated and user contributed system for checking URLs for the presence of Viruses, Trojans, Worms, or any other software considered Malware