I got a call supposedly from the IRS stating I needed to call them or else I'd get a warrant for my arrest... I believe all legit IRS issues would be sent via registered mail not a threatening phonecall. Scam.

I got a call from a supposed Officer Hoffman that I was under investigation by the IRS and that there was a warrant out for my arrest. The caller said it was very important that I return their call immediately that day. The interesting thing is that they didn't even salute me by my name. That's a dead giveaway to me that it's something shady. I tried calling back (blocked my ID on my cell) and the line was busy. I could not get through. I think a real officer would have call waiting or the official number to his office where I could leave a vm. I call [***].

Got a call from an "IRS" agent. Said a warrant out for my arrest. Did not call me by name. Generic message. Did not call back. I'm 99.9% certain this is not legit

There is a widespread IRS (or CRA) or "tax scam" being  practiced by scammers on both USA and Canadian residents.

USA tax payers should read this:
http://www.irs.gov/uac/Newsroom/Phone-Scams-C ... 5-Filing-Season

Canadian tax payers should read this:
http://www.cra-arc.gc.ca/nwsrm/lrts/2013/l131210-eng.html

Short answer:
The IRS never initiates a contact via phone.
They always send a snailmail first.

Educational post:
This scam is also described as scam #11, here:
http://phonehelp.2truth.com/facts.html

If you were contacted by an IRS impostor, you may file a report, after clicking on this link:
http://www.treasury.gov/tigta/contact_report_scam.shtml

UPDATES:
Recent news story:
http://www.wltx.com/story/money/2015/03/12/fa ... -scam/70202814/

Congressional hearing:
http://www.nbcnews.com/business/taxes/tax-imp ... hearing-n341906

Received call from 210-880-4826 from so called IRS officer Jack Hoffman. Called  him back later in the day and there is no greeting message telling the office hours, or anything official, just generic message that the  customer cannot be reached at this time. What IRS agent gives out their personal mobile phone number for business. This is a scam.