The federal government has contacted “dozens” of Australians whose Medicare card numbers were illegally sold on the so-called dark web.

It’s believed someone breached the security surrounding Medicare details, potentially exposing Australians to fraud.

Federal police and cyber security authorities are now investigating the “traditional criminal activity”, which was revealed on Tuesday.

A report on The Guardian website detailed how one of its own reporters was able to buy his Medicare card number from a dark net trader for less than $30.

Human Services Minister Alan Tudge declined to elaborate on the official investigation, before citing previous cases of doctors’ surgeries being broken into.

“I have my strong suspicions but we’re leaving it obviously up to the police to do a proper investigation,” he told ABC radio on Wednesday.

Mr Tudge again admitted the government wasn’t aware Medicare details were being sold on the dark web for several months.

But he insisted personal health records aren’t at risk and those saying otherwise were indulging in fear-mongering and being irresponsible.

“Someone hasn’t hacked into a database,” Mr Tudge said. “There is no indication this is widespread.”

At least 75 files are believed to have been sold since October last year.

However, Mr Tudge couldn’t confirm this saying only that the government believed the number of those affected was a “small number in the dozens”.

“The people that we know had a Medicare card number breach, we have contacted,” he said.

Doctors are seeking government assurances that patient records are secure.

“This is a deeply concerning,” Australian Medical Association president Michael Gannon said.

The AMA fears the Medicare issue might dissuade Australians from taking part in the government’s My Health Record online patient health information program.

“It is so important for the success of the My Health Record that doctors and patients both have absolute confidence in the integrity of the system,” Dr Gannon said.

My Health Record stores information such as allergies, medical conditions, treatments, and scan reports.

Almost 20 per cent of Australians have signed up to the scheme since it was launched in 2012.

A digital file will be established for every patient next year, unless they opt out of the scheme.

Dr Gannon said it was important Australians used My Health Record.

“The electronic health record has the potential to reduce adverse drug reactions, to prevent allergic reactions, to reduce unnecessary duplications of investigations to save the system money,” he said.

A spokesman from the Health Department said My Health Record has multiple layers of security to protect access to the system.

“My Health Record has been in operation for over five years, with nearly 5 million Australians having a record, and in this time there have been no security breaches of patient data in the system,” he told ABC.