Visual Editor inserts an empty <p>-element containing a <span> for every post

[PoPSiCLe]

Main problem, apart from the fact that this is a completely unnecessary element (or, rather two elements) is that it inserts the SAME code over an over (once for each post) with the SAME #ID:

<p><span id="hwContLayer" style="background: gray none repeat scroll 0% 0%; overflow: auto ! important; position: absolute; left: 0px; top: 0px; width: 5px; height: 100%; z-index: 10000000; opacity: 0; font-weight: bold ! important; font-size: medium ! important; font-style: normal ! important;"> </span></p>

[Denis-de-Bernardy]

Can't find any reference of hwContLayer in WP. It's probably a browser toolbar, or maybe a virus.