On a more fundamental level, I wouldn't trust NIS to protect my PC/XT running
IBM DOS 1.1! It's the most useless AV ever released, and literally anything
else would be better.
The only reason it has such a large market share is because of 'push
marketing' in the shape of forced preinstalls.
AVG, Avira, Kaspersky, Avast, NOD32, any of those should do the job. Norton
corporate version is (surprisingly) pretty-much OK, it's the home versions
that suck. Other two which are possibly none too great are Panda and McAfee.