@aladdinsane - hackers may hate Microsoft but they're not top of the tablet (or mobile phone) league. Anything which gets millions of users can be a target... As Windows is popular, it gets attacked. There have been attacks on other systems, and despite what some say, even Apple kit can be hit by malware.
With Windows systems, I tend to scan once a quarter with Trend-Micro's Housecall (run from the browser, downloads a bit of software, scans your system, reports results in the browser), even though I generally have AVG and get it to scan and update every day.
It's always possible some 'nasty' will be spotted by one firm and takes a while to be detected by another anti-virus, and as they may name the same thing differently (because they are often similar to some previously identified malware) it's sometime confusing if one AV calls it different to another... but if it's detected and can be removed, that's a part of the battle won, anyway!