A man says he is out of pocket by more than $1200 after his bank declined to refund fraudulent transactions on his credit card after he didn't report them in time.

The Auckland resident, who doesn't want to be named, said he applied for a visa card with the ASB bank at the end of 2016 to go on a trip to America.

After the trip he used the card infrequently and made top-up payments to cover the minimum repayments.

It wasn't until 18 months later when he looked closely at the statements that he discovered a series of fraudulent transactions dating to back to February 2017.

The transactions included payments made in Chinese Yuan and US and Australian dollars for purchases ranging in value from just a few dollars to several hundred dollars as well as exchange rate conversion charges from the bank.

"As I was not using the card and just adding funds to the credit card account I never noticed any discrepancies. Foolish on my behalf, yes."

Two months ago he reported the problems to ASB but was shocked to find the bank would only refund the fraudulent transactions going back to January this year - an amount of $157.

"ASB told me they could only go back to January 2018 and if I wished to dispute the amount I should contact Visa.

"The amount taken from my credit card account was almost $1200."

The man said he was surprised the bank had not picked up on the transactions itself and likened the situation to entrusting property to a storage facility which then took no responsibility when the property was stolen.

A spokeswoman for the bank said it was unable to comment on an individual customer's situation but took the security and protection of its customers very seriously.

"We have sophisticated fraud detection systems in place," she said.

"We encourage our customers to be vigilant in relation to their accounts and transactions, which includes reviewing their bank account and credit card activity regularly, and reporting any unauthorised activity to the bank."

The spokeswoman said if a customer believed a transaction was incorrect, they needed to notify the bank in writing within 30 days of the closing date on their statement to enable the bank to investigate the transaction.

"If we are not notified we may be unable to reverse the transaction."

In an email on May 18 from ASB the man was told the bank had "lost the right of appeal" through Visa International to reverse the transactions which were billed to his account before January 2018.

The ASB spokeswoman said in order to dispute a transaction it had to follow Visa processes and the 30-day time limit was designed to ensure it met the dispute time limits imposed by Visa.

"Timeframes may vary depending on the circumstances, but in general queries or disputes on credit card transactions need to be raised by the card issuing bank within 120 days".

The man said he wasn't aware of the 30-day limit until he checked the fine print and frequently asked questions online.

Consumer New Zealand head of research Jessica Wilson said banks themselves had a responsibility to look out for fraudulent transactions.

She said sticking hard and fast to the 30-day rule didn't seem fair and she would expect the bank to give its customers some leeway to report fraud.

Given many of the transactions were made using foreign currencies Wilson said she would have expected the bank to pick up on them.

"That is the kind if unusual activity - offshore transactions - I hope they would be able to pick up on."

Wilson said people who regularly used their cards to make online purchases should check their statements frequently.

She urged people to check their statements every month before paying their bill.

Wilson said people also needed to be cautious of which websites they shopped at online.

"Check the site is secure. If you are handing over a lot of money do your due diligence."

The situation comes after it was revealed last month that ASB had received an "unprecedented increase" in disputed transactions which the bank put down to the growing number of online transactions.

Last week the government's Computer Emergency Response Team said it had received a record 506 reports on cyber security incidents in the first three months of this year.

Of those 168 were incidents, scams or frauds designed to convince a user to giving up money.

How much time do you have to report a fraudulent transaction on a credit card?

We asked all the major banks how much time their customers have to report fraudulent activity on a credit card and this is what they said:

• ASB - 30 days from the statement date.

• ANZ - 60 days from the date of the disputed transaction.

• BNZ - 30 days from the statement closing date but can consider claims outside of that on a case by case basis.

• Westpac - up to 30 days from the statement date but it may consider taking claims outside of the 30-day period on a case-by-case basis.

• Kiwibank - 120 days from the transaction date to raise a dispute.