(Symantec) is as good as any other well known anti-virus program, it is costly, requires numerous services and running processes that consume system resources and often results in complaints of high CPU usage. Anti-virus software components insert themselves deep into the operating systems core where they install kernel mode drivers
that load at boot-up and create files/folders/registry entries in various locations.
I have read from other users that Norton has made improvements in newer versions of their software so they are not as resource heavy as past versions...while others still say differently. Those issues plus the cost factor are the primary reason many folks look for a free alternative. IMO, Norton is better utilized in an Enterprise system environment
protecting many client computers. With that said, there are a lot of folks who prefer using Norton (especially if it came preinstalled) and there is nothing wrong with staying with a product you are satisfied with.
Norton Security Standard, Deluxe and Premium (formerly Norton Internet Security) are suites which means they include 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.
I'm not an advocate of suites. All-in-one tools and suites are filled with extra features (including "bells & whistles") which typically use more system resources than separate programs that do the same task while other suites leave a much smaller footprint. Suites tend to have varying degrees of strengths and weaknesses accorded for each feature they incorporate. Internet Security Suites include a Firewall component, which IMO is unnecessary since the Windows built-in firewall is one of the best
and provides adequate protection
. Further, many folks also use a router which is essentially a hardware firewall.
In contrast, separate tools are designed, built and maintained with a greater focus in a specific area so they are generally of better quality and more effective at what they are designed to do. This means the program's performance for that particular feature is usually superior than their all-in-one counterpart. Further, all-in-one tools generally do not allow the user as much flexibility in tailoring program settings and usage.
If you are adamant about using a suite, then I would recommend one of the following:
See my comments at the bottom of Supplementing your Anti-Virus Program with Anti-Malware Tools
as to why I recommend Emsisoft.