Fraudsters have hacked into the Royal Agricultural Benevolent Institution’s telephone system and run up costs of £4,700.
The grant-making charity, which supports the farming community, said it wanted to warn other charities about the scam, known as ‘phone phreaking’, which left its phones down for two days and families in need unable to contact its confidential helpline.
Hackers targeted the charity’s head office in Oxford and one of its residential homes on the weekend of 30 November by cracking voicemail codes and then dialling a premium-rate number.
RABI said the number was thought to be based in Russia and set up especially to carry out this kind of fraud.
The charity’s telephone provider noticed the unusual activity and blocked calls to and from the charity. But the institution was already £4,700 out of pocket after just five hours.
Paul Burrows, the charity’s chief executive, said: "As an organisation we take security very seriously, but it seems that all it took was for someone to guess a voicemail code at random.
"We now understand this kind of fraud costs UK businesses at least £16m a year. I should like to warn other organisations and especially other charities to be on their guard in case it happens to them too.
"We were fortunate that our service provider noticed the unusual telephone activity and barred calls before we lost even more money. Other people might not be so lucky. It’s clear we all need to remain vigilant and increase the security in our phone systems."Since the incident, the charity has blocked all premium-rate numbers, both UK and international, as part of measures to protect it from such crimes in future, a RABI spokeswoman said.