I just received a voice mail from Adam with the same run down as noted in other posts. I JUST watched something on Thursday night regarding this scam! Yes, it scares people initially. Just remember, anyone who is unwilling to send this type of communication via certified mail is not credible.
My wife received the call on her cell phone from "Adam Peterson" (Asisan accent) and he said our son should call him back, claiming it was a "legal emergency." Said he was from the Department of Legal Affairs for the U.S. Treasury." I called the number and got a greeting from a "John Marshall." Asian accent. I work for the U.S. Dep't of Justice. Sounds totally phony to me.
I got the exact same call just 30 minutes ago. There is no Department of Legal Affairs for one. Then after very little sleuthing, the IRS rarely phones, preferring to send many letters first. While it did raise my heart rate, I agree it's a scam.