When considering data corruption I would suspect packet fragmentation. This is hard to troubleshoot except to try setting the MTU on the affected router (e.g. your internet router) to lower values, and try again.
I would start by finding a consistently problematic site, and use that as your test. Then remove all intermediate routers and connect your computer/laptop directly to the source of your internet, and see if that solves it.
This might help: http://www.tolaris.com/2010/04/08/troubleshooting-path-mtu-problems/