Israeli spies planting software into the police national computer network with a USB stick to steal secret files is possible - but highly unlikely, according to a forensic technology expert.

The Security Intelligence Service ordered a check on the police system as part of an investigation into the alleged suspicious activities of Israeli groups during and immediately after the Christchurch earthquake.

But police are confident the National Intelligence Application (NIA) was not compromised.

The Dominion Post yesterday quoted an anonymous source about concerns that an Israeli search and rescue team could have inserted a USB drive into a police computer and loaded a program allowing remote backdoor access to the NIA.

That scenario is possible but subject to several conditions, according to Barry Foster, who heads the forensic technology team at Deloitte.

A former senior analyst with the police Electronic Crime Laboratory, Mr Foster said hacking into a computer network was "limited only by imagination and technical ability".

While a USB device could upload code, Mr Foster said the breached computer must be connected to the NIA and a police officer logged on.

"So any spy would have to have physical access to a computer within minutes of a police officer walking away, have permission to plug in a thumb drive [USB] and do so without anyone noticing," he said. "It's possible but probably not plausible."

- staff reporter