By Tony Hanson

PHILADELPHIA (CBS) — Telephone con artists around the country continue to target grandparents, preying on the emotions of these vulnerable victims. A Nigerian man living in Canada was recently sentenced in federal court in Philadelphia to 45 months in prison for cheating grandparents in the United States and in Canada.

The scam works like this; a person gets a call from someone impersonating a grandson or granddaughter in trouble, they need money urgently for bail or medical care, and the grandparents should wire it or use a credit card.

Sabina Keller, of Philadelphia, recently got such a panicked, but phony call from someone pretending to be her grandson. The story was that he and some friends were stopped by police in Canada and drugs were found in the car.

“He seemed upset,” Keller says. “He seemed very upset, very anxious.”

The caller identified himself as Reds, a nickname used by Keller’s grandson. The voice wasn’t familiar, but he claimed to have a cold, and demanded secrecy.

“He said ‘Please don’t call my dad, please don’t call my mom,’” Keller says. “I said ‘what is going on?’ He said ‘they are going to hold me. I need $2,500 bail.’”

But Keller paused when a bail officer got on the line and requested the payment by credit card, over the phone.

Keller’s instincts were good. With red flags waving and bells going off, she made up a story of her own. Keller said she needed to talk it over with her husband, got a callback number, and then quickly called family and determined her grandson was okay, and that this was a scam.