The number of illicit websites customized for portable devices has surged roughly 20 times over the two years to March, a survey said Sunday.

The total was 57,000 as of March 31, up from 2,900 two years ago and 19,000 the year before because security awareness is lower among users of smartphones and tablets than with PC users, the survey by security software firm Trend Micro Inc. said.

Designed to steal money or personal information, most of the bogus websites masquerade as porn sites and charge false fees or sell counterfeit goods.

The most recent cases targeting mobile devices are bogus Facebook and Twitter sites that steal IDs and passwords, it said, putting people's private information at risk.

"Because portable terminals are great sources of private information, there is a danger that contact info for family members and friends will get stolen," a Trend Micro official said.

"People should consider smartphones as small PCs rather than mobile phones," the official said, urging users to be aware of the danger of visiting illicit websites.

Trend Micro confirmed 25 million instances in which illicit sites were accessed by portable devices in Japan during the quarter ending in February, it said.