I found out someone applied for a mortgage loan under my name, What can be done ?

I applied for a new Verizon plan, and in their credit check process they asked me that May of 2010 a mortgage loan was applied - which bank holds your loan - Which I answered by None of the above. The credit got approved - but I am scared if there really is a Mortgage applied under my name. Last year end of april I moved to SF and lived at a rental property. I have never applied for a mortgage. What can I do about this ? Are mortgage loans that easy to get in case of an ID theft ?