Microsoft stopped supporting the enormously popular OS almost three months ago, but according to the newest figures from Web tracking firm Net Applications, more than a quarter of PC users still relied on XP in June.

XP remains resilient despite Microsoft's multi-year upgrade campaign, which included frequent reminders that the OS would become vulnerable to malware, and even a zero-day scare shortly after Microsoft ceased support. The latter pressured the company to issue a security fix in a "one-time exception" to its support policy.

Net Applications, which scans a network of 40,000 websites and 160 million unique users each month, found that Windows 7 remained the top OS overall, with 50.55% of PC users. That was up meaningfully from 50.06% in May and 49.27% in April. Retailers and OEMs have deemphasized Windows 7 in their consumer offerings, but Net Application's new numbers reinforce that among businesses that recently upgraded from XP, most chose Windows 7.

Windows XP remained the second most popular OS by a large margin. It snared 25.31% of users in June -- basically flat compared to May. XP commanded 37.17% of the market in June 2013 and more than 29% in January, which means that millions of XP users have indeed upgraded to newer platforms.

But millions still remain, and XP's rate of attrition is slowing. Some businesses are paying Microsoft for extended XP support, and many third-party security vendors offer XP-oriented products and services as well. Consequently, not all of the XP traffic, which is drawn from users who connect to the public Internet, necessarily represents the same security risk.

Windows 8 and 8.1's flat-lining growth speaks to why Microsoft's older OSes remain so popular: Existing Windows customers simply haven't felt compelled to upgrade. In June, Windows 8.1 accounted for 6.61% of the market, up a bit from 6.35% in May. The original version of Windows 8 held 5.93%, down from 6.29% the month before.