(Norton) is as good as any other well known anti-virus program, it requires numerous services and running processes that consume system resources and often results in complaints of high CPU usage. I have read from other users that Symantec has improved the newer versions while others say differently. However, Symantec products can be difficult to remove and remnants are often left behind which require the use of a special removal tool, otherwise you may encounter problems installing a replacement anti-virus. To be fair, other vendors are also using removal tools for the same reason. Those issues plus the cost factor are the primary reason many folks look for a free alternative.
Norton Internet Security is a suite which means it includes additional features
, in addition to anti-virus protection. Some of those extra features will also consume resources and affect performance. Symantec Endpoint Protection includes many of the same features but is intended for small businesses with several computers and servers.
Keep in mind that no single product is 100% foolproof
and can prevent, detect and remove all threats at any given time. Just because one anti-virus detected threats that another missed, does not mean its more effective. The security community is in a constant state of change as new infections appear and it takes time for them to be reported, samples collected, analyzed, and tested by anti-vendors. Security vendors use different scanning engines and different detection methods such as heuristic analysis
or behavioral analysis
which can account for discrepancies in scanning outcomes. Depending on how often the anti-virus database is updated can also account for differences in threat detections.
Further, each vendor has its own definition of what constitutes malware and scanning your computer using different criteria will yield different results. The fact that each program has its own definition files means that some malware may be picked up by one that could be missed by another. Thus, a multi-layered defense using anti-spyware products (including an effective firewall) to supplement your anti-virus combined with common sense
, safe computing
and safe surfing habits
provides the most complete protection.