Can a Windows 7 Home Premium serial key be activated more than once in different computers?

I have installed Windows 7 Home Premium in my computer and activated it.What happens if someone stole my key.Can the thief activate windows 7 home premium on a different computer using the key which i am using already without contacting Microsoft?Can i activate windows if i reinstall using the same key after this?
@kingkrunal
thanks for the advice but i dont need serial keys as i have the genuine one.I asked this question because i was afraid if someone stole my key.