An 89-year-old woman has been conned out of £100,000 by "callous" scammers posing as bank officials and police.
Warwickshire Police said the victim was told there was a problem with her bank, which the bogus officers were investigating, and then tricked her into transferring the cash to another account for safe keeping.
The elderly woman, of Atherstone in north Warwickshire, believed she was talking to officers from the Metropolitan Police and her own bank.
Officers said the woman had been deliberately targeted and are now warning people to be on their guard against similar scams being carried out nationwide.
Detective Chief Inspector Sean Paley said: "While people are generally aware of such scams, these criminals target vulnerable members of the community.
"I would urge people to talk to close friends and relatives who they think could be at risk."
Police have urged everyone to check callers are genuine and be suspicious of unsolicited phone calls.
People should never give out personal details to callers unless absolutely certain of their legitimacy, officers said.
Anyone who suspects they have been targeted should call police on 101.
For further information, call Crimestoppers on 0800 555 111, or visit www.crimestoppers-uk.org or www.actionfraud.police.uk.