The scumbags and lowlifes figure by putting someone's American-sounding name (David Adams) and having a recording of a computer-generated voice you'll be fooled.  Too bad they don't have anyone who can speak English on the other end of the line when they start their "we're the IRS and we're going to arrest you" spiel.  This is just another attempt to bilk gullible people out of their money.  The US government never initiates legal actions over the telephone - that's the only clue you need to determine if the caller is real or not.