Configuring preferences and options in Outlook.com
Huh, that's strange... You're absolutely sure it's not attached to anything? You MIGHT be able to find something under the Outlook settings (that cog on the top right), clicking More Mail Settings..., and hunting around there for a solution.
Just to be sure there's no accounts or anything attached (I'm clinging to this since it's the only thing I know), you should take a quick look at the Content from third-party networks section, and toy with the settings there. More specifically, the 'Showing Public Content' area. Clicking Don't Show also helped me out.
You never know, it could help you. If you've already tried it, then.. yeah, I've got nothin.