ACT police are asking for help identifying a woman who brazenly robbed an elderly woman at a Woden ATM.

Around 11:35am on Friday the 79-year-old woman was withdrawing money from the cash machine when her purse was stolen by a younger woman.

The purse was found a short time later, but a sum of money was taken.

Sergeant Daryl Neit says crimes against vulnerable citizens are reprehensible.

"To prey on the fragility of a senior citizen is one of the most cowardly acts imaginable," he said.

"I urge anyone with information about this offender to come forward to the police.

"Crimes against the most vulnerable citizens in our community will never be tolerated by ACT Policing or the public."

The elderly woman was unharmed in the incident.