Farmers posting cheques have been fleeced of more than $100,000 as thieves take advantage of the rural mail system, police say.
They are encouraging cockies to switch to internet banking after investigations which started in the Coromandel revealed it was a countrywide problem.
Rural residents alert posties there is mail to pick up by raising small flags on their mail boxes.
"What we've found however, is that offenders targeting cheques being posted to pay bills are getting to these mail boxes before the postie and then stealing the cheques," said eastern Waikato area commander, Inspector Dana McDonald.
The thieves then amend the amount the cheque is written out for and try and cash it at banks some distance from their victims' homes.
"When you think about it, for dishonest people, stealing cheques is pretty easy. All you have to do is take note of the mail boxes with flags raised and get to them before the scheduled postie's run, Insp McDonald said.
"Initially properties on the Thames Coast Rd north of Thames and further south towards Ngatea were affected with thieves cashing in cheques to the value of about $12,500 at a time but since then, speaking to colleagues in other districts we have identified victims from around Auckland, Taupo, Palmerston North and Canterbury."
Sixteen victims had been identified so far, losing around $100,000, but Insp McDonald expected more stations to report more thefts.
"There is however, a simple way to prevent this and this involves paying your bills and accounts electronically using password-protected internet banking."