Since the IRS is not in the business of protecting you from the theft of your social security number and it would seem they are mainly interested in collecting taxes from any available party, the protection rests with you.

Of course I recommend monitoring your credit report among other preventative and protective actions (see this page for more protection strategies) but since this type of identity theft isn't evident on your credit report, I also suggest that you review your Social Security Earnings Statement that is sent to wage earners every year approximately two months before their birthday.

The earnings statement can alert you to additional earnings reported under your social security number that you did not actually earn (but will be expected to pay taxes on!).

Click on this link (and then scroll down to item #6) if you need to report inaccurate earnings or fraud associated with your social security number.