In a police interview played at the Old Bailey, Elizabeth Curtis, of Cornwall, said she was duped into transferring money from her bank accounts by callers pretending to be police officers.
Yasser Abukar, Sakaria Aden, Mohamed Dahir and Ibrahim Farah deny conspiracy to commit fraud.
All are in their 20s and from London.
A fifth defendant, Mohamed Sharif Abokar, also in his 20s and from London, has pleaded not guilty to converting criminal property.
In the police interview, Miss Curtis said she had received a series of phone calls from people claiming to be police officers who told her she had been the victim of bank fraud.
She followed their instructions to transfer her money into account numbers given to her by the callers, she added.
She said she was stunned to learn the calls were bogus and felt stupid to have been taken in.
The court has heard that the alleged Â£600,000 fraud involved 18 pensioners from across the south of England, including Cornwall, Devon, Dorset, Bedfordshire, London and Kent.
A 73-year-old woman broke down in tears as she described how she lost Â£130,000 in an alleged phone scam targeting pensioners.