Update April 26, 2013: Both Twit.tv and Hbo.com have now been removed from the Internet Explorer Flash blacklist.

Microsoft released a new Internet Explorer 10 Compatibility View list this week.

Normally, that’s not news. But this one contains a little piece of history: the first-ever blacklist of domains that aren’t allowed to run Flash content in Internet Explorer on Windows 8 or Windows RT. Previously, sites containing Flash content had to earn a place on a Microsoft whitelist for playback. The new policy allows any site to play content unless it's on the new blacklist. (For details about Microsoft's sudden change in heart, see "Microsoft changes default Flash behavior in Windows 8 and RT." )

I was curious about which sites would make the blacklist and finally had a chance to inspect it today. The new CV list is remarkable in two ways.

First, it contains only a dozen domain names, one surprisingly large and another surprisingly well known in tech circles.

Second, it’s mainly focused on Flash on ARM – in other words, Windows RT and its signature device, the Surface RT.

Here’s a screen shot showing the entire <NoFlash> portion of the list:

It’s a little surprising to see HBO’s website (hbo.com) on the banned list, just as it’s odd to see Leo Laporte’s online media empire, Twit.tv, there. But a closer look at the old and new CV lists shows that both sites were already restricted to x86 and x64 devices. In fact, an ARM-only version of the blacklist had already been part of the previous list, with these mostly high-profile sites approved for Flash on x86/x64 devices but not authorized on ARM.

Of the 12 entries on the Microsoft "Dirty Dozen Flash Domains" list, nine are banned only from playback on ARM devices. A grand total of three domains are banned from using Flash on any Windows platform. The website at Briggs-riley.com, for example, shows off some of the best luggage in the universe (I'm a huge fan and longtime customer), but apparently their web designers aren't so good with Adobe tools.

If you’re a fan of Twit.tv (where my ZDNet colleague Mary Jo Foley is a regular), everything works fine on Windows 8. On Windows RT, you’ll be shunted seamlessly to an HTML5 version of the site if you try to watch published shows. I had no problems watching back episodes of Leo and friends on a Surface RT. The live stream, however, requires Flash and does not currently work on Windows RT.

But if you try (as I just did) to visit HBO on a Windows RT-powered device, you’ll be stopped at the front door.

It’s a very iPad-like experience. Thankfully, it’s one you won’t see too many other places in Windows.

On an x86/x64 PC running Windows 8, things work much differently in the immersive, modern-style Internet Explorer. HBO's Flash support with that class of processor is just fine, as you can see from this screen snippet.

It's worth noting here that HBOGo.com, the site you're most likely going to visit to play HBO shows on a PC or tablet, works fine on Windows RT and is not blacklisted.

I’ve asked Microsoft, HBO, and Twit.tv to comment on the list and will update this post as needed.