free antivirus software

I agree with others here, AVG free is really the best. I have been using it for about two years. I never have a problem with it conflicting with other programs and that used to happen to me all the time with Norton. Also I love it that it runs automatically everyday at the same time. Although this slows down my machine for a bit, I don't really mind because I expect it and a couple times it has saved me big problems by finding a virus or trojan right away. It also scans all my e-mail. The other great thing is that it updates automatically as new dangers arise.

Most of the free ones are fine, AVG is one of the better ones IMHO.

BUT
You do get what you pay for in life, and if you pay nothing, well, it speaks for itself.

A year ago I tested a few of the freebie AV's.
For example I installed AVG, went to a site where I knew viruses where rife, got myself a little infested and AVG found nothing

Scanned and it found some trojans etc.
Then I uninstalled the AVG and installed Kaspersky, it immediately found 3 other trojans that AVG didnt find
And I dont mean "POSSIBLE" trojans that the software deemed "MIGHT" be a trojan
they where known trojans

I tried a few other free ones and even NOD32, which I think is pretty good and is rated well around the net
Same story as AVG
NOD32 found some, some more with a full PC scan
but uninstall and installed Kaspersky and rescanned and more where found by Kaspersky
Maybe other paid AV's will have found them as Kaspersky did, but personally I rate Kaspersky as the best there is (no, I have no affiliation with them whatsoever)
They are not free, but IMHO they are the best you can get.

As far as I'm concerned, the free ones are ok for average users looking at B&Q garden furniture and checking their bank balance and a few emails (etc)

But anyone who uses the internet extensively, by that I dont mean in dodgy websites, I mean is in and out of many different websites all the time, downloading various software for whatever use (business trials etc) then you want something more secure with a better heuristics scanning.

Stay away from Norton like the plague, was great before symantec got their grubby hands on it and tried to take over peoples PC's.
Anyone who knows about PC's will tell you why Norton AV is rubbish, in many ways!

If you have the cash available get something decent to protect your PC. As I said, free ones are ok, but the paid ones are far better.
How does AVG give out a free AV software, AND charge for a paid one?
Fairly obvious really!

The paid ones libraries are much more up-to-date with the current definitions, and the heuristics scanning is usually far better.
When a virus/trojan is found and is becoming known amongst the reports in all the AV companies, they update their virus definition library.
A decent paid AV software's heuristics scanning will find potential viruses/trojans BEFORE the virus/trojan definition list is updated.

Freebie scanners are not as good for this detection level, and usually spyware and adware is found more often with the paid software.

Explaining how companies can issue free AV software and at the same time the same company can charge for AV software.

Dont let me put you off though, as I said, NOD32, AVG and a few others are good enough for general PC/internet usage.
I use Kaspersky internet protection
Which is a AV scanner and firewall all in one
If I download a virus it knows immediately. I got something the other day in a RAR file, I knew it wasnt a virus as my friend was working on something, but the scripts in the file in the zip archive COULD be deemed as a security threat
Kaspersky wouldnt let me even unpack the RAR file until I told it the file was ok

And I checked with shields up for the firewall checking

Quote: Your system has achieved a perfect "TruStealth" rating. Not a single packet — solicited or otherwise — was received from your system as a result of our security probing tests. Your system ignored and refused to reply to repeated Pings (ICMP Echo Requests). From the standpoint of the passing probes of any hacker, this machine does not exist on the Internet.

Quote: All attempts to get any information from your computer have FAILED. (This is very uncommon for a Windows networking-based PC.) Relative to vulnerabilities from Windows networking, this computer appears to be VERY SECURE since it is NOT exposing ANY of its internal NetBIOS networking protocol over the Internet.

Quote: One or more ports on this system are operating in FULL STEALTH MODE! Standard Internet behavior requires port connection attempts to be answered with a success or refusal response. Therefore, only an attempt to connect to a nonexistent computer results in no response of either kind. But YOUR computer has DELIBERATELY CHOSEN NOT TO RESPOND (that's very cool!) which represents advanced computer and port stealthing capabilities. A machine configured in this fashion is well hardened to Internet NetBIOS attack and intrusion.

And thats only with the Kaspersky settings on standard, there is another mode .. "stealth" so IMHO it's doing the job perfectly