This week, Microsoft issued patches for 79 flaws across its platforms and products. One of them merits particular attention: a bug so bad that Microsoft released a fix for it on Windows XP, an operating system it officially abandoned five years ago. There’s maybe no better sign of a vulnerability’s severity; the last time Microsoft bothered to make a Windows XP fix publicly available was a little over two years ago, in the months before the WannaCry ransomware attack swept the globe.