If you already have a windows license but lost your installation media, you can download it without resorting to piracy. The link below has the URLs for the retail ISOs hosted by Amazon. http://www.mydigitallife.info/windows-7-iso-x86-and-x64-offi...
The official solution is to buy an additional copy of the Windows license which will provide you with a new download URL.
I knows this because I complained to the @microsoftstore twitter account: after purchasing 2 copies of Windows (the crapware-loaded OEM version, the clean one from MS store) I had no intention of purchasing a third.
For some reason they simply couldn't allow me a second download, and sent me a physical disc, which arrived about 6 weeks later, by which time a pirated Windows 7 was working fine.
However