A young mother was convicted after using the internet to declare a relationship she was concealing from welfare authorities.

Mt Maunganui's Lauren Kaney, 22, had told Work and Income New Zealand that she was single, picking up $480 a week in benefits as a solo mum.

But investigators who scrutinised her Bebo and Facebook pages found the truth: she was living in a relationship with the father of her 2-year-old son, entitling her to only $140 a week.

The Ministry of Social Development confirmed last night that it has an eight-strong intelligence unit using tools, such as Facebook and Bebo, to chase down fraud tip-offs.

The disclosure comes as the Minister of Social Development Paula Bennett signals a tougher stance on benefit fraud. She has called on ministry staff to prepare a report on the issue, which costs taxpayers about $60 million a year.

The case also reveals the extent of the "cocoon effect" - the belief among some people that information they put on the internet is not going to be viewed by the wider public.

Kaney told the Herald on Sunday that she knew she was not entitled to $17,500 of benefit money she was convicted of taking. She admitted misleading a social welfare officer and providing misleading information, and was sentenced to four months' home detention and 200 hours of community service in the Tauranga District Court on Friday.

Kaney said WINZ began investigating after getting a tip that she was living with her partner Jason McConachy.

"Then they looked at my Bebo page. It came as a big surprise when I was caught. I didn't ever think they would look me up like that. It's not really fair of them to do that, but it wasn't fair of me to rip them off in the first place."

Kaney said she told WINZ she was single, claiming the domestic purposes benefit and accommodation supplement for her and her 2-year-old son for over a year. For most of that time, she was living with McConachy.

Kaney said she was not motivated by greed but was trying to pay off debts and manage bills. "I'm not a gambler or a drinker. You hear of people ripping the system off for their addictions, whereas my benefit was going on rent, power and food."

Kaney said four months of home detention was daunting, and her sentence had not hit her yet. "But at least I will be home with my son and I can look after him."

She warned that it was not hard for beneficiaries to take advantage of the system. "It's way too easy if you want to do it. The temptation is there. If they (WINZ) don't want it to happen they need to do something more about it. ..."

"I just want people to know I'm not a bad person, I just did what I had to do to get by."

Kaney is back on a benefit - she now gets about $380 each week from WINZ, which includes an accommodation supplement. She receives a further Family Assistance payment of $86 per week from the Inland Revenue Department.

Paula Bennett said she would not tolerate benefit fraud and this month called for a report from Ministry of Social Development chief executive Peter Hughes. "The Government believes welfare is a safety net for those who truly need it," she said.

Justine Auton, general manager of integrity services at the ministry, said its Wellington-based intelligence unit included internet searching as part of its efforts to combat fraud.

"We've been using any information we can ever get our hands on for years - Facebook as long as it's been around."

Netsafe director Martin Cocker warns internet users that everyone is being watched. "It's hard to have sympathy for someone caught out because of putting information up but it does point to the value of these tools to help cross-reference people's stories."

Barrister Karen Harding said if someone was writing personal information on a website they became "fair game" to investigators.