In the US, many new machines will be delivered with "trail versions" of McAfee on them, so I've seen it in some detail a few times. With the last version I had, however, a visit to the McAfee site for a support issue resulted in so many advertising popups and other trash on the machine that I needed an "anti-McAfee" to clean up the machine. I've heard that they've improved their website, but their ratings in reviews were "averae" to "mediocre" and variable for several years.

I avoided the common complaint that Norton AV "slowed down the computer" by being on dial-up during that phase, and my net connection was so slow that any impact from the AV was undetectable. Their last few versions have been rated as "very fast" and with consistently high ratings on effectiveness by trustable reviewers. Coupled with the permission to install most retail versions on three machines for one purchase/subscription, it's not free but is quite reasonable - if you have multiple machines, and support that I've needed has been excellent. While I can say that I've been quite satisfied with them, there are equally valid other opinions.

Several of the free AV programs have received excellent reviews, but none that I've watched have consistently stayed in the top tier as the threats change - at least for the free versions. Paid versions of several have been consistently reviewed as being quite good.

Most of the AV makers recommend that you do a complete uninstall of all prior AV installations before installing a new one, or a new version of an existing one. All Norton programs that I've seen automatically remove any prior version of Norton before beginning the new install, although it appears that they'll leave anything from another maker (but might ask if you want it uninstalled?).

Any time a problem with an AV is indicated, it probably is a good idea to do a complete uninstall of the AV on the machine, before a clean install of the one you intend to use. "Patches" and updated signature files should be okay, but any version change - even if it's just called an "upgrade" - likely should be done as a clean install.

Of course "always" is always subject to exceptions, except when it's not.

It may also be noted that although the Internet is truly "international" there have been some notable differences in the specific kinds of threats most common in the US vs what people in "those other places" are most likely to see, so it is quite possible that what's best here may not be optimum in Slovisburpistan - or other places I'm not sure I can spell.

John