Ministers are to focus on cutting the £2 billion cost of benefit over-payments in the latest advertising campaign to reduce the welfare bill.
Claimants who find a job or move in with a partner are being asked to tell the authorities to avoid a fine of up to £2,000 or prosecution.
In the last full financial year, over-payments because of an error by claimants - often because their circumstances had changed but they had not told the authorities - reached £1.6 billion, while the cost of errors by officials stood at £700 million.
By comparison, the total cost of benefit fraud - where claimants have set out to defraud the tax-payer - was £1.2 billion in 2012/2013.
As part of the advertising campaign, posters will be put up asking: "Claiming benefits? Got a new job? Make sure you tell us. We're checking benefit claims."
Sources at the Department for Work and Pensions (DWP) describe the new campaign as a "softer" approach.
There will also be posters aimed at encouraging the public to report suspected benefit fraud.
They state: "When you report a benefit fraud we investigate it. If you know someone claiming benefits who shouldn't be, call us. Help us catch benefit cheats."
There will also be adverts in newspapers and on Facebook, while letters will also be sent to claimants to highlight the importance of notifying the authorities when circumstances change.
The campaign will last between four and six weeks and is being piloted in six areas. They are: Southwark, Blackburn, Hounslow, Blackpool, Epping Forest and Cardiff.
Welfare Reform Minister Lord Freud said: "It is only a small minority who commit fraud but it costs the country over £1 billion a year.
"We are keen to make sure that claimants know that even small over-payments can really add up over time, so they must get in contact with us and let us know about changes in circumstances straight away.
"The new pilot campaign will help us stop fraud and overpayments before they even happen."
Claudia Wood, deputy director of think tank Demos, said: "No one can excuse benefit fraud and it's really important that people know to tell the DWP when their circumstances change, so they are not inadvertently receiving too much in benefits.
"But you have to question the wisdom of this pilot - 'report benefit cheat' posters and the hotline already exist, with 96% of calls categorised as malicious and just a 1.3% success rate.
"Targeting specific locations with a communications blitz is a replay of last year's ineffective 'go home' illegal immigrant vans and may do little more than stigmatise genuine claimants entitled to and in need of benefits."