Eiji Ishikawa, chairman of computer security firm Artemis, said in an interview on Wednesday. Two record, stole personnel files and added links to pornographic sites.
Experts say the rush has led to a lack of necessary precautions against unwanted intruders.
He welcomed the government's recently announced steps to tackle cyber-crimes, saying they should help Internet security businesses such as Artemis, but he said they were long overdue. Since the hacking raids, Japanese ministries have set up task forces of experts to find ways to prevent future attacks and the Tokyo Metropolitan Police has launched a new task force to combat Internet crimes. Earlier this month, a law prohibiting various forms of improper access to computer networks also went into effect. Ishikawa said the knowledge of hacking and preventing it were the two sides of a same coin, but cautioned that for hackers, the lure of breaking into an Internet site remained strong. It's like a video game.