A Hamilton woman who defrauded the National Bank of more than $110,000 via an internet banking loophole has been sentenced to 12 months in jail.

Airiana Moana Paul, 20, had earlier pleaded guilty to 13 computer crime charges of dishonestly obtaining a pecuniary advantage at the Hamilton District Court, the Waikato Times reported.

She was part of a group which discovered a loophole in the bank's online system last year.

Over a three-month period, she defrauded the bank of $112,037, making 365 fraudulent transactions and actively drew others into the online scam.

Paul told police she came across the banking loophole by accident and accessed various online accounts through internet cafes around the city, and one in the public library.

She made multiple transactions, transferring money from an online National Bank account into another account, despite there not being enough money in the original account.

If transactions were made late in the day, the transfer could not be reversed until the following day. That left a small window of opportunity in which transferred funds could be withdrawn.

By the time the bank was aware of the scam more than $400,000 had been fraudulently transferred, leaving it $200,000 out of pocket.

During sentencing yesterday, Judge Robert Spear said Paul's offending was premeditated and calculated.

Paul's actions represented major fraud and was "cynical offending in the extreme", he said.