A computer virus dubbed “Gumblar” is wreaking havoc with Internet users, directing them to harmful sites and embedding malware via hacked Web pages.

According to Internet security firms, there are more than 3,500 cases of Gumblar Web page infection in Japan, and the independent Information-Technology Promotion Agency (IPA) has called on Internet users to beware.

IPA says that Gumblar works by first stealing the administrator passwords for company and personal Web sites from computers where they are based, allowing penetration of the sites. If an illicit user then rewrites some of the site HTML code, visitors” computers can be redirected to other sites which may further infect their computers with malware that can facilitate the download of harmful programs.

According to Internet security company Kaspersky, Gumblar infections came to their attention around May and June last year, and increased suddenly in the autumn, with major firms such as East Japan Railway Co. (JR East) and Honda Motor Co. revealing late in the year that their company sites had been affected.

At the beginning of this year, it was discovered that the home page of the Tokyo branch of the Democratic Party of Japan had also been altered by Gumblar, while convenience store chain Lawson and the Keio railway company announced Wednesday that their home pages had also been infected.

Kaspersky says that if a computer has all of its software updated to the latest versions, then it should not be redirected to the malicious sites even if a user is viewing a Gumblar-infected Web page.

“Check that all your software is up-to-date, and if not, make sure to get the latest version,” Kaspersky advises. Users can check to see if their software is up-to-date at the Web site below.