A Jersey campaign to prevent people claiming benefit they are not entitled to has had more than 250 reports of suspected fraud.
The Social Security department launched the "Benefit Thieves - Let's Stop Them" campaign in March.
Those making false claims could have to pay back any excess, have their benefit stopped or reduced or be prosecuted.
The department said one woman had been sentenced to 15 months imprisonment, suspended for two years.
It said she was told to repay £18,000 she received after failing to inform them that her partner had moved in.
Deputy Ian Gorst said: "By the courts handing down a sentence of this severity, it makes clear to the general public that benefit fraud is not tolerated."