Update #2: Rumor has it Staples will be doing free offline updates for anyone who wants one.
Update: Launch date is 7/29! Reserve your free upgrade now.
Microsoft just announced today that not only will they be offering the new Windows 10 (set for a "summer" release), as a free update for current Windows 7, Windows 8.1 and Windows Phone 8.1 users, they will also be giving it to users currently running pirated copies of their software.
This article suggests this is a way to re-engage with the Chinese market, where an estimated three-fourths of all installed software is pirated.