Dear,
Mostly the accuratesse of virus software isn't depending of definition files, but also
some patches to your EXE influence the way it is working.
Also for heavy stations with advise to use two or more scanners. What the first is missing
will be catch by the other. Of course the software and definition files must be
up to date also.
An advantage is too, when your software can control your email system also.
greetings.
