They can't be stopped.  They are hard core scammer/extortionists located in India.   You can protect yourself.  Invest in a call blocker and don't pick up on numbers you do not recognize.

Just had a call from this number today.  Said he was Officer Something or Other with the IRS.  That I or my attorney must return the call immediately.  Very heavy foreign accent.  I knew it was a scam but dialed the number anyway.  He answered with just a "Hello."  I explained that I was returning a call from a scam artist and was promptly hung up on.  I called back and went direct to voice mail.  His voicemail identified him as Office Whomever with the IRS but alas, the mailbox was full.  I would have liked to have left him a message.

This guy said his name is officer James Smithers and he is with the IRS and threatened legal action with a foreign accent and said if we do not call back by ourselves or by our attorney for an urgent matter and would not tell what the matter is from an unknown line.

This is a scam from some Islamic terrorists. Just ignore.

If more info matters to you, read: http://800notes.com/Phone.aspx/1-202-241-7314

http://www.irs.gov/uac/Tax-Scams-Consumer-Alerts
http://800notes.com/forum/ta-8c2f64bf2b91fa5/irs-warns-of-telephone-scam

Report the Calls to the real IRS here:
•report the incident to the Treasury Inspector General for Tax Administration at 800-366-4484.
•You can also file a complaint with the Federal Trade Commission at FTC.gov. Add "IRS Telephone Scam" to the comments in your complaint.

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Do consider maybe getting a call blocking device or phone.. You can google them and many are around $50.00 or so.