Is this a corrupt wordpress install?

I installed wordpress and I am getting the following line code inserted in the editor every time I go to make a new post:

 

<iframe id="__jquerycheck" style="display: none;"></iframe>

The editor opens up clean, but when I toggle between the Visual and Text tabs the line gets added in somehow. Sometimes I get stacks of them 3 or 4 high.

I have turned off all my plugins and switched themes and it still shows up. No idea where it might be coming from. Any help appreciated…