It’s a common enough technique that this surely isn’t the only example, but there was discussion here a while back about TeamViewer doing this to detect the pre

It’s a common enough technique that this surely isn’t the only example, but there was discussion here a while back about TeamViewer doing this to detect the presence and version of the client software when clicking a link to open a remote session: https://news.ycombinator.com/item?id=32165103 https://news.ycombinator.com/item?id=32165103 In their case, the (shell of a) font file goes a little further and encodes the version of the teamviewer client that installed it