In recent years, one of my most common fixes when peeps bring in their computers for repair is to remove Norton, Trend Micro or McAfee. Most common symptom is unexplained 90+ % CPU usage which usually results from a 3 month trial that came with a new PC and has now expired, that somehow mysteriously disappears as soon as the Norton / Trend Micro / McAfee processes are shut down in Task Manager. But have to say that I haven't seen this in almost two years ....cant say it don't happen any more just that I don't see many people using either of them anymore.
The free ones are OK if you are willing to put up with:
1) The manual update requirement.
2) The need to use separate malware and firewall programs.
We're not very insistent on what people use, there are numerous good products out there. But the three I recommend most are:
Checkpoint Software's ZoneAlarm Internet Security Suite ($40 for 3 PC's)
http://www.zonealarm.com/security/en-us/zonealarm-computer-security-suite.htm
Bit Defender Internet Security Suite ($70 for 3 PC's)
http://www.bitdefender.com/solutions/internet-security.html
http://www.av-test.org/no_cache/en/tests/test-reports/test-reports/?tx_avtestreports_pi1[report_no]=114803
Kapersky Internet Security ($80 for 3 PC's)
http://usa.kaspersky.com/products-services/home-computer-security/internet-security
http://www.av-test.org/no_cache/en/tests/test-reports/test-reports/?tx_avtestreports_pi1[report_no]=114864