404 errors in the Symfony2 logs caused by an "OPTIONS" http request

Question

We delivered some times ago in production a Symfony2 project. In the prod.log file we have that 404 error quite a lot of time:

[2012-10-17 13:10:03] request.ERROR: Symfony\Component\HttpKernel\Exception\NotFoundHttpException: 
No route found for "OPTIONS /bundles/mythemes/css/" 
(uncaught exception)at /data/apps/project/webapp/version/app/cache/prod/...

It is normal as a user can't parse the CSS directory, a valid URL is for example:

/bundles/mythemes/css/ie7.css

I have found an issue on the Symfony2 tracker that is also about a bad http "OPTIONS" query:

https://github.com/FriendsOfSymfony/FOSRestBundle/issues/142

I am just wondering what is causing this error.

Answer 1

I found the source of the problem, in these cases the referer was "Microsoft Office Protocol Discovery". It is all explained in this post:

What are "Microsoft Office Protocol Discovery" and "OfficeLiveConnector" and why do they access invalid URLs?