(Symantec) is as good as any other well known anti-virus program, it it requires numerous services and running processes that consume a lot of 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. Further, there have been numerous complaints about lack of sufficient support from the vendor.
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 (Symantec) 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.
Choosing an anti-virus is a matter of personal preference, your needs, your technical ability and experience, features offered, user friendliness, ease of updating (and upgrading to new program release), ease of installation/removal, availability of quality/prompt technical support from the vendor and price. Other factors to consider include detection rates and methods, scanning engine effectiveness, how often virus definitions are updated, the amount of resources the program utilizes, how it may affect system performance and what will work best for your system.
I generally recommend ESET NOD32 Anti-Virus
or Emsisoft Anti-Malware
if choosing a paid for program as they leave a small footprint...meaning they are not intrusive
and do not utilize a lot of system resources which slow down performance. Kaspersky Anti-virus
is also a good choice for the same reason. If you don't want to pay, then I would recommend either Sophos Home Free Antivirus
or Bitdefender Anti-virus Free Edition
if you prefer not to use Windows 8/10 Defender
For other anti-virus alternatives, please refer to Choosing an Anti-Virus Program