More than 13 million personal computers in Japan will be exposed to higher risk of virus and other attacks starting in mid-April, experts warn.

These computers are still running the Windows XP operating system, which Microsoft Corp. will stop supporting entirely on April 9.

An estimated 7.23 million Windows XP-based PCs are still in use by companies, accounting for 20 percent of all PCs in Japan. Migration to newer operating systems, such as Windows 8.1, has been slow, especially at small and midsize firms, because managers are either unaware of the problem or want to avoid the cost of updating.