Can you have more than one resident Anti-virus program running in real time?
Can you? YES
Should you? NO
Is it a good idea, do you get better protection? NO
The danger, is that one antivirus program may (read this as eventually will)
see the others definition files as viruses, and will remove them. This is not so much a problem with manual scans, where you only run one Antivirus program at a time, if you pay close attention to what it detects, and where. If you manually configure it to ignore the other program, and its files, then you minimize the risk from this problem.
The big problem, is the silent threat. Most antivirus programs will scan web based (not necessarily all, like P2P, and IM) file transfers. It is quite common, for one antivirus program, to detect the incomming virus updates for the other. Thinking parts of the definition files are viruses in their own right, the AV will strip these out of the update.
The end result? Instead of having two, or even one, up to date fully functional antivirus programs, you have two severely crippled programs, which are each missing critical definition, and detection files .
So, it is best to have one antivirus program, and keep it up to date and use it properly.
Then, if you experience a problem, or question its efficiency, you run an online scan:BitDefenderhttp://housecall.trendmicro.com/