Comic book artists and industry officials expressed concern Tuesday about the potential for illegal distribution on the Internet, pointing to cheap and simple technologies that could spawn homemade bootleg factories.

"We don't know yet whether the case is the tip of the iceberg, but there are strong possibilities that similar cases will emerge," Hiroshi Katsurayama, a legal official at the Association of Copyright for Computer Software, told a news conference.

He was referring Tuesday's arrest of three individuals suspected of posting "manga" comics on the Internet without permission.

The trade group banded together with manga artists and publishers to help police catch the operator of the offending Web site, known simply as 464.jp.

The site's existence came to the attention of manga industry officials around September, they said, and the operator had been warned repeatedly that it was violating the Copyright Law.

"Protecting the renowned comic culture of this country is important for the future of Japan as an intellectual property powerhouse," said Shihei Yamazaki, a lawyer for the manga artists' group.

For publishers, the illegal digital distribution of scanned comics presents a huge threat to a budding but highly promising online publishing market.

"We estimate the total online publishing market will come to around 9 billion yen for the year to March, and comics will account for some 5 billion yen of it," said Tetsuro Daiki, an official of the intellectual property management section at Shogakukan Publishing Inc.

He said the publishing industry is set to expand online distribution to both cell phones and computers, given growing demand for reading manga on computer screens.