one hundred percent.
You wouldn?t expect one medicine to treat dermatitis, stomach ulcers, heart problems, and diabetes. They are all maladies and all bad, but they are all different and require different drugs. Similarly, you need different treatments for different computer malware. You need one thing to treat viruses, another to remove spyware, another to catch Trojans, etc.
Sometimes you need more than one drug to treat a problem, other times one is sufficient, and two would interfere with each other, even to the point of becoming dangerous. Similarly, one software firewall is all you need and is all you should run. (You can have a hardware firewall in a router along with your one software firewall.) Remember, any software firewall slows down network communications, and two would slow it down even more with no appreciable benefit. Windows XP has a built in firewall, but it protects only against incoming activity. If you should somehow get a Trojan that sends information out, you are not protected. Get a better, two-way, firewall and disable the Windows firewall. I use ZoneAlarm (free version).
Similarly, I feel strongly that two antivirus programs should not be running together. In some cases they will cross interfere; but even if they don?t under normal circumstances, wait until they both discover a virus. They will fight over what to do about it, and this could lead to serious system problems. I would not even have two installed. If you do, you must turn one of them off every time you boot ? and this is a pain. Microsoft says that you should not have two antivirus programs in any Windows operating system. What you should do, is get the antivirus program you trust the most, and run it alone. If you ever suspect it has missed something, or if you want to double check, run an on-line virus check from a different company; there are several. Currently I am using Avast (free version) and then use housecall for online scans.
Two, or even three anti-spyware programs can be used together, and are desirable because none catch all such malware. (I won't go into the reasons here.) But beware! There are dozens of programs out there claiming to be anti-spyware; many are not very effective, and some are actually the opposite of what they claim ? they plant spyware. For more information on rogue anti-spyware, go to
Also look at his list of trustworthy ones -- all five of them. I use three of the free ones Spybot Search and Destroy, Ad-aware, and Microsoft Antispyware Beta. Unlike antivirus, these programs do not run constantly in the background, hence they do not interfere with each other. You run them one at a time when you want to remove spyware.
Neither antivirus nor antispyware are very effective against Trojans. Therefore, you should have protection for this malware. Trojan Hunter is considered one of the best, but costs $50. A Squared (the name is actually a subscript 2, which cannot be written here; it is not A2 squared as suggested by rosepawn1) is considered good, and costs only $30. I don?t know any good, free antitrojans at this time.
Important fact: No antivirus program remains effective unless its database on your system is up to date. No virus waves a flag to your AV saying ?I am a virus;? your AV program must look for a footprint, or signature, and compare it with those of known viruses. If there is a match, then you are notified. Sometimes people complain that their AV didn?t catch a virus; often that was because they did not keep up to date.
There are times a virus is not detected because it is a brand new type of virus, and possibly no AV program would have caught it. New viruses show up daily, many with new signatures. When a new virus is discovered, it takes a little time to identify it and its signature. This information must then be added to the database, and you must download it. This may take from one to a few days. This is why you should check for AV updates daily. Antispyware is in exactly the same category.
I have some comments specific to rosepawn1?s post. ZoneAlarm Security Suite is a good package. It has an excellent firewall (the inferior Windows firewall should be disabled), pretty good (but not the best) antivirus, antispyware whose rating I have not found, and several other features. However, I would not run both Avast and the ZoneAlarm AV; but this is a personal decision. I just hope that, if a conflict arises in the future, blame will not be assigned to either ZoneAlarm or Avast.
A Squared is an adequate antiTrojan at a rather fair price, and I am happy to see that such software is included. AntiTrojans are overlooked by most.