So here is the scoop. I bought a copy of Windows 8.1 Pro (Full version) off eBay in October last year. I thought I did enough due diligence, the seller had a long eBay history with no negative comments. I also phoned Microsoft to check the license was legit and they confirmed as much. Just today MS revoked my license so I called them and they confirmed the key had been used on multiple computers. The seller has since had their eBay and PayPal account suspended and I suspect this is the reason why. I have opened a case with PayPal and fully expect to get my money back, if PayPal don't play ball I intend to do a credit card charge back. So what to do now? I want a copy of Windows to run games under Bootcamp so virtualisation is out of the question. I figure my options are:- 1. Buy a copy of Windows 8.1 from MS for £180. This is really not going to happen. At this price I really feel like they are pushing me into using illegal software. It's particularly galling knowing they only charged £30 when it was released. 2. Just keep buying copies from somewhere like eBay and hope I get a good one. If each copy gets me 4 months use before being revoked I can still buy 6 copies before I pay as much as what MS charges (stupid huh?). And Win 10 will be out well before then. 3. Stick two fingers up to MS and just find a dodgy key, it would serve them right for charging mental money. 4. Load my 5k Retina iMac with Windows 10 now, and therein lies my question. Have you installed it on your 5k? Is it currently stable? Any things I should be wary of? Is Bootcamp compatible? Can I upgrade straight from my current install? Thanks.