Crimes involving the use of the Internet jumped 58.7 percent to 319 cases in the first half of this year compared with the same period last year, reflecting surges in online prostitution and transaction fraud, the National Police Agency said Thursday.

The number of cases that involved buying sex with minors jumped to 46 in the January-June period, up from only one in the first half of last year. In all but one case, sex was bought via Internet personal advertisements.

Internet scams, including swindling cash via online transactions, also increased to 53, up from 25. Of those, 32 involved online auctions.

Other Internet-related crimes investigated by police included 55 possible violations of child pornography rules, up from 49, 18 cases identified as libel, up from 13, and 10 cases deemed copyright violations, down from 12.

High-tech crimes, including Internet crimes and other illicit online transactions involving bank networks, totaled 365 for the period, up from 234.

The agency also said police detected 959 cases of unauthorized access to computers and computer networks by such means as using someone else's password.

This is a sharp increase from the 106 cases in the period from February 2000, when the law banning unauthorized access came into force, through December 2000.

Of the 959 cases, 418 are thought to be from overseas while 165 originated in Japan. Police could not identify the origin of the other cases.

Police opened investigations on only 17 of these unauthorized access cases, apparently indicating the difficulty of establishing a case for high-tech crimes.