system
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From the download page - System Requirements
[b]Operating Systems Supported[/b]
Windows 7
Windows Vista (any Edition excl. Starter Edition)
Windows XP [b](Service Pack 2 or higher)[/b]
BTW, XP SP1 has been unsupported by MS for ages and XP SP2 since July 13, 2010. You are not getting hotfixes for critical Windows vulnerabilities. You seriously can’t rely on an AV or security suite to make up for this fact.