Ars Technica:

Audio device maker Sennheiser has issued a fix for a monumental software blunder that makes it easy for hackers to carry out man-in-the-middle attacks that cryptographically impersonate any big-name website on the Internet. Anyone who has ever used the company’s HeadSetup for Windows or macOS should take action immediately, even if users later uninstalled the app.

If you’ve ever used this software, you should fix/patch it immediately.