Singapore has seen fewer illegal immigrants and overstayers over the past few years, but the number of people caught providing lodging to immigration offenders rose sharply last year.
One factor, said Immigration and Checkpoints Authority (ICA) senior investigation officer Roger Leong, is that immigration offenders are moving out of the usual "hotbeds" such as Geylang and Little India into areas such as the heartland.
Also, while five or six immigration offenders might be putting up with a single landlord four years ago, offenders are now "dispersed" and tend to stay in smaller groups of up to three people, said Assistant Superintendent Leong.
According to ICA statistics released earlier this month, 416 people were arrested for providing lodging to offenders last year, up from 250 in 2014. Those caught providing work to immigrant offenders also rose, to 91 from 69, over the same period.
Criminal lawyer Rajan Supramaniam said ignorance and negligence could lead to landlords not carrying out their due diligence and checking with the relevant authorities.
"Often, offenders may have forged their work permits, or had them terminated before their expiry dates," he said. "People unfamiliar with the rules may be convinced that these are legitimate."
He added that sometimes, landlords do not check as they are taken in by people who pose as employment or real estate agents to show foreigners around.
Said criminal lawyer Shashi Na- than: "Some of these harbourers may be willing to take the risk because they are getting rent in compensation."
This is worrying as the minimum punishment is a jail term, he said.
"We need to educate the general public more on such offences."
In one case, Er Chiang Hee, 44, collected $18 daily for renting out bedspace in a four-room private apartment in East Coast Road for about two months last year - this cost him six months in jail.
Er, the caretaker of the apartment, was told that Vietnamese national Le My Ron, 34, had just arrived in Singapore. He decided to rent a bed to her in August last year without checking her permit or pass, or details of the documents against that of her passport.
Le's visit pass had actually expired earlier, in June last year.
Er, who was sentenced last Wednesday, had also been harbouring another Vietnamese woman, who was 44 years old.
With offenders possibly spread out across Singapore, said ICA senior project manager of community partnership Wong Kong Wa, it is difficult to spot immigration offenders among legitimate workers.
He added that ICA intends to step up its public education.
Dr Tan Wu Meng, who sits on the Government Parliamentary Committee for Home Affairs and Law, said: "Overstayers and illegal immigrants can cause security problems for home owners and neighbours."
Added Dr Tan, an MP for Jurong GRC: "In addition to the security risks, if immigration offenders go unchecked, it could undermine the respect between locals and legitimate migrant workers."