title: Web fonts not loading on IE11 on Windows 10 Pro
body: <p>I have a site that uses web fonts.The site used to function properly until the client's IT team rolled out Windows 10 Pro across the organization. After the Windows  upgrade, the web fonts stopped working with error "CSS3111: @font-face encountered unknown error" on IE 11 browser. However on all other major browsers including new Edge the site works without any issues.
  I did some search to and came to know it is because of a recommended features called  <strong>Untrusted Font Blocking</strong> and to disable it I need to modify certain registry keys. However in my case that is not an option as the <a href="https://blogs.technet.microsoft.com/secguide/2017/06/15/dropping-the-untrusted-font-blocking-setting/" rel="nofollow noreferrer">this feature is recommended by Microsoft for security</a>. Also it needs the change to be done on local machines.
  While googling, I noticed some people suggesting encoding and embeding of font file as Base64 encoded string. In fact I could see that as a workaround in many Q&amp;A sites and forums (eg <a href="https://stackoverflow.com/questions/33608481/ie-and-font-awesome/44529306#44529306">here</a>, <a href="http://dakehe.info/blog/post/windows-10-block-untrusted-fonts" rel="nofollow noreferrer">here</a>). But I failed when I attempted to do that. On my Win10+IE11 I still get <strong>CSS3111: @font-face encountered unknown error</strong> (screenshot)<a href="https://i.stack.imgur.com/GLyDa.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GLyDa.png" alt="enter image description here"></a></p>
  
  <p>Further googling led me to <a href="https://stackoverflow.com/questions/35856032/why-dont-base64-embedded-fonts-work-in-ie11-if-font-download-property-is-disa">this SO question</a> that actually answers to my problem. It says even if I convert the font file to Base64 the Win10+IE11 will still prevent it while converting and loading into the memory for execution.</p>
  
  <p>Interestingly I found major Font and icon vendors are not attempting to figure out a workaround for this as I can see none of their website shows up properly on Win10+IE11. Even Microsoft's own site (outlook.office.com) has this issue.</p>
  
  <p>Now my questions are:</p>
  
  <ol>
  <li>Is there any workaround that can help me to fix the issue</li>
  <li>If no workaround then is it a good idea to have a end user warning popup to switch to more supported browser with user agent detection?</li>
  </ol>
  
  <p>Thanks in advance.</p>