Virus Programs and Computer Stability
If you by chance Install two virus scan programs there is a serious threat of system instability. I did it with ENOD 32 and McCafee and experienced problems. So always uninstall one Virus program before Installing the other, to keep your system safe and agile in response time.
The system instability also occurs because both the programs become Memory Resident and take up your valuable resources in RAM just not freeing up enough space for your regular programs