Police insist a web-scanning tool which allows them to monitor people's movements is not a case of Big Brother watching.

The software, Signal, developed by Wellington company Intergen with police collaboration, means wall posts, photos, videos and status updates sent from major events are likely to be viewed by police.

Police say the real-time information - scanned from Twitter, Facebook and YouTube - helps prevent crimes and increases public safety.

Intelligence director Mark Evans said Signal sped up the ability of police to analyse social media feeds related to crime and public safety. It was first trialled during the 2011 Rugby World Cup. "It [Signal] allowed us to search through relevant public posts more quickly."

If social media users have geo-location enabled on their smartphones, police can also map where the messages are being sent from.

Mr Evans said the software was not invasive. "It can't see private communications between users."

He said much of the internet was a social platform, and police need to be aware of what is going on.

Intergen marketing director Wayne Forgesson said the product was "a handy tool" for the police.

Police use Signal to search for hashtags and keywords, enabling them to monitor large groups. During the World Cup they used Signal to intercept a boy-racer convoy from Auckland to Hamilton that was to coincide with a match, and learnt quickly about a planned protest.

A spokeswoman from the privacy commission said it appeared the software was only accessing public web postings.

Contact Sam Boyer

Consumer Affairs reporter

Email: sam.boyer@dompost.co.nz

Twitter: @SamJBoyer