I used w3 total cache on my Multisite install.
For a reason I didn't understand, I was hacked, and when someone was going to one of the website, the visitor was redirected to porn websites. Only on mobile devices, not on standard computers.
I removed w3 total cache, deleted the cache folder, etc. and the bad redirections disappeared.
However, now, when someone is visiting one of the websites, the content is correct but the CSS is not loaded. So the websites look ugly.
Did I miss to clean something after w3 total cache removal ?
You can have a look at the problem on at http://libre-factory.com