Someone calls from this number and leaves a message on the phone informing that there is a criminal investigation against you with IRS.

After you call them, they start reading out some rubbish to let you know that you are in trouble with IRS.

I started talking to the guy - telling him that I know all about this fraud and I won't buy it. He said that he is calling from Pakistan and has nothing better to do but do this work to scam people.

It is a pity that these people are poor, but outrageous that they are trying to scam Americans. They target immigrants who are more vulnerable.