Unfortunately, ID theft is a common concern for many of us. The Federal Government has put together a useful website to assist in dealing with the issue here.
Sahil Patel was the ringleader of what the IRS called the largest impersonation scam in the agencies history. Although this group of scammers was shut down at the end of 2013, there are many others out there operating similar scams, trying to scare people into giving them money and/or personal information. For more information here’s an article on the subject or you can go to irs.gov.