>Can someone remind me what the options are for free antivirus programs, for home use - and perhaps a suggestion, which is best?
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>I have been using AVG for some years now, but the version I am currently using makes my computer very slow, and I can't even update to the latest version, recently announced - I get an error message every time I try.
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>Using Windows XP.

Stop using AV in real-time scanning mode - they cannot keep up with the rate at which new variations are being developed. Rather go for weekly AV scans, personal firewall software, anti-malware mainly for the browser (like Windows Defender) and common sense.