Japan's largest price comparison Web portal, Kakaku.com, said Trojan horse programs were installed on the company's servers during an unauthorized intrusion on May 11. The company detected the intrusion soon after it occurred. Instead of closing the site, Kakaku.com decided to keep it open until May 14 in an attempt to trace the hack, company president Yoshiteru Akita said at a news conference in Tokyo Wednesday. The Trojan programs have been identified as "trojandownloader.small.AAO" and "PSW.Delf.FZ," and can affect PCs running Windows 95, 98, ME, XP, 2000, and NT operating systems, Kakaku.com said. Delf is a Trojan program that installs a keystroke logger and remote control software. The programs record all keystrokes made on an infected PC. If a PC gets hit and the user logs into a server, the attacker can get the user's password for the server and access the user's account. The company said the site wouldn't be back in operation until May 23 at the earliest.