Although McAfee is as good as any other well known anti-virus program, 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. If you do a Google Search
you will find there have been numerous complaints about it affecting system performance. Those issues plus the cost factor are the primary reason many folks look for a free alternative as a replacement. Further, IMO, McAfee is better utilized in an Enterprise system environment
protecting many client computers.