This person claims to be Officer Kevin Peterson from the IRS.  Their supervisor is Officer Julie Smith whos phone number was identified as potentially fraudulent:

http://800notes.com/Phone.aspx/1-415-506-2406

They sounded very convincing so I sent them money via pay vouchers (which should have tipped me off!).  So please be wary and make sure you investigate your sources, etc.

correction to the link above:

http://800notes.com/Phone.aspx/1-415-234-9613

I just got a call from this number saying they are from the US treasury Office. A legal action has come against me that they had sent me a registered letter about a class action against me. I was to call an officer Jack Conowy for details. This is crap and a scam to send them money! this is a harassment! The number the woman gave me to call (who could barely speak engilish) is the same number she called from. 415-505-2406

Same as above.  Live in midwest.  Had alot of info on me, to include my tax preparer.   Called my tax person to verify there was not a breach.

Just got a call from this number (Ashley) who wanted my wife - insisted that I take a message.  Same as above - IRS -  says that a registered letter had been sent last month, blah, blah.  What is really worrisome though is that the caller used my wife's nickname, not her legal name and the caller also knew my nickname.  Of course, IRS would never know either of us by other than our legal names so this scam couldn't work, however if this was a more personal scam - say asking for ransom it could have had a chance of working.....