There is a fairly common IRS or "tax scam" being practiced by scammers in both Canada and the USA.
USA tax payers should read this:
http://www.irs.gov/uac/Tax-Scams-Consumer-Alerts
Note particularly the links at that site, warning of the scam!

the caller claims to be an "officer" from the IRS.  does not have specific details about whom the are trying to reach.

I like to find out who is behind this no