I would shy away from installing any antivirus on 844/X. For no other reason than they can take away system resources and throughput when you're meant to be working - especially if you've got it turned on to scan in the background.
It could result in frequent stops when playing back video.
The best thing would be to keep your system away from the internet. :o)
If that's not an option and you do install an antivirus, just make sure that it runs only when you expect it to rather than constantly in the background.
This is just an opinion, so YMMV.
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