Born in Windows 3.1, died Windows 8. The hosts file, which contains redirects from URLs to IP addresses, has been a fixture of online computing since the days of the ARPAnet. Windows, OS X, iOS, Android, Unix, and Linux all have variants of the hosts file. Windows 8 has a hosts file, but Windows Defender protects it in an odd and as yet little-understood way. Apparently if you add entries to the hosts file manually, Windows Defender may remove the entries in some circumstances, even if the file is marked read-only. We’re still waiting on details from Microsoft.