Japan has more than 550 internet-based dating services and some 80% of the people who accessed them use mobile telephones, figures from the end of February show.
Lack of regulation In the first six months of this year, 793 web-related crimes were reported, compared with 888 for the whole of 2001.
Crimes linked to internet dating services in Japan have more than doubled in the first six months of this year, the National Police Agency has said.
But the number of internet-linked crimes could actually be much higher, and police admit there are difficulties in tracing some crimes due to the lack of regulation.
"Right now, it is difficult for us to crack down on illegal internet dating crimes as there is no specific law on such services," a police spokesman said.
Internet-enabled mobile phones were reportedly used to access the dating sites in almost all cases.
Web-based dating sites - the online equivalent of lonely hearts columns - have become increasingly popular in Japan, especially among the more than 55 million users of internet-equipped mobile phones.
In a well-publicised case last year, a high court judge received a suspended sentence for paying schoolgirls for sex after contacting them over the internet.
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