@ tigerstriper
Well still puzzling as the file name is still a mystery, the path you show doesn't include the actual file name, the WinSxS (Windows Side-by-Side) directory/folder can be massive, so it could be like looking for a needle in a haystack without the details. See
http://blog.tiensivu.com/aaron/archives/1306-Demystifying-the-WinSxS-directory-in-Windows-XP%2C-Vista-and-Server-20032008.html and
http://www.winvistaclub.com/f16.html.
The detection isn't saying for certain that it is a rootkit, but a hidden file and there could well be a legit reason for that but no one can say if that might be the case as we don't have the full path and file name. You should be able to expand the column width (drag the column separator to the right or double click on the column separator) so you can see the full details.
So it is entirely possible that considering the nature of the WinSxS folder, there may well be a hidden .dll file running, but that can't be confirmed as we don't know the full folder location and file name.
In short, Winsxs, which stands for ‘Windows Side By Side’, is Windows native assembly cache. Libraries which are being by multiple applications are stored there. This feature was first introduced, in Windows ME and was considered as Microsoft’s solution to the so-called ‘dll hell’ issues that plagued Windows 9x.
I'm not sure this needs specialist intervention until it is identified if there is a problem and 'hidden file' as opposed to a definitive detection isn't a clear cut infection.