Netsafe says cyber attacks on New Zealand businesses are becoming more sophisticated.

It comes after Christchurch business, Leeding Sign Designs was forced to cough up almost a thousand dollars to an overseas web site that encrypted its files on its computers.

The email remained unopened, but the virus still managed to get a foothold.

Director Darren Leeds said it led them to a website which demanded a ransom.

"And then they put a countdown clock up on the screen of the computer, and we had a140 hours to pay $500 US, and then that amount doubled."

Darren Leeds said he sought advice, but was told he had no other alternative but to pay them.

"The encryption of the virus was unbreakable, so we went to go to use our backups, and our backups had been destroyed as well. As the day went on, it got worse and worse."

Netsafe digital project manager Chris Hails said 50 ransom-ware attacks were reported to them last month alone, and the problem is only getting worse.

"If you have an android smartphone or an android tablet, it can lock up that device, and that's becoming quite nasty." He also warned of a new form of attack, which can "change the pin on your phone."

Chris Hails said people need lines of defence, that includes anti-virus, back ups and staff training so they know how to spot a dangerous file.