Microsoft Corp. stops providing free support for the Windows 7 operating system Tuesday, and warned that an estimated 13.9 million computers in Japan still using the system could become more vulnerable to viruses and hacking.

According to Microsoft's Japan unit, an estimated 7.53 million computers in Japanese offices and local government facilities and 6.38 million in households are still using Windows 7, comprising around 20 percent of all active Windows computers in the country.

With the end of support, users need to upgrade to Windows 10 or other operating systems. They should also consider buying new computers as older machines may not be compatible with the newer software, the company said.