I recently saw this type of dangerous scam on the news.  The caller poses as a government agency (in this call it stated they were the IRS and were preparing to file a lawsuit against me and I better call them right away!)  If you call back someone will attempt to convince you that some small amount of ourstanding tax, parking tickets, etc. are owed and will ask you to pay via MoneyGram or other cash transfer system.  Beware.