Many users think that running multiple protection programs simultaneously will make their computer more secure. The truth is, running multiple protection programs may in fact increase the risk of infecting your computer. Some types of protection software that users double up include firewalls, antivirus and anti spyware scanners, and real-time virus scanners.

Why shouldn't a user use multiple firewalls?

In some cases, you can get away with running two firewalls. However, in a number of cases, running two or more firewalls will cause connectivity issues. I have seen a number of users install third party firewalls and lose their internet connection. When investigating the issue, I usually find that the user has previously installed another firewall or two, or that they are using a router that has a built in firewall. The loss of connectivity results when the different firewalls try to filter and block the same connection and can get confused and either block each other from working correctly or block the internet connection completely.

These days, firewall protection is all over the place. If you have Windows XP with Service Pack 2, you will have the Windows Firewall, and if you get high-speed internet, you may even get firewall protection from your service provider, as well. Then there are the Protection Programs that may come installed on your computer, such as McAfee and Norton, that include firewalls. Additionally, built in firewalls come installed on many routers to help protect your computer from internet attacks. Before installing multiple firewalls, I would recommend that a user check to see what they already have installed and try to determine the compatibility between the different firewall programs that you have installed and any firewall you may be considering installing.

Can a user run two real-time scanners at the same time?

Yes, in most cases you can. I, however, would not recommend it. Running two real-time scanners will drastically affect your computer’s speed. When you have two scanning programs running that are programmed to scan every file accessed on your computer, it will take a ton of your computer’s processing speed to run both applications.

I have seen many users try to run two real-time or "on access" scanners, only to find their computer running so slow as to be almost rendered useless. When we would turn off one of the scanners, it made a huge improvement on the user’s system, and it worked better, as well. When two on access scanners were running, it either took too long to scan the file or the two scanners would conflict with each other, allowing an infected file to slip by both scanners. It seems that the best practice would be to use one on access or real-time scanner per system, rather than two or more.

Will a computer be more protected if the user runs multiple virus scanners?

This may be a touchy subject, but I would suggest only running one antivirus and antispyware scanner at a time. A user should be very careful when choosing to use multiple malware scanners, as they can conflict with and remove each other, rendering one, if not both, inoperable. This happens more often between the free scanners than the well known, paid for scanners. If you choose to scan your computer with more than one malware scanner of the same type (virus, spyware, adware, etc), I would suggest running them at separate times. If you run them both at the same time, it will take up entirely too much of your computer’s processing speed and may not allow either of the scanner engines to run at all.

When running multiple virus and spyware scanners, try to pay attention to the file that is being tagged as a "virus" or as "spyware." You may be surprised to find that it is detecting another scanner’s files. This is referred to as a false positive (FP). This false detection is quite common and happens most frequently because of the manner in which the file works. I often see a scanner engine’s detection files being tagged – this is due to the manner in which that file is used to find the virus or malware on the computer. There are also a lot of bogus scanners out there, most of them installed by other malware, that will try to detect a number of bad files to try to get a user to purchase the software needed to clean their computer – when, in fact, the computer is clean.

As a general rule of thumb, I would suggest only using one firewall program, one real-time or on access scanner, and one or two virus, spyware, and adware type of scanners. Doubling up on protection software often does more harm than good. Each program has a specific job it tries to do, and running two or more only causes them to get in the way of each other.