NOTE: please do not click on the links and report back that "nothing happens." That is what people have done on other forums. I am not trying to "get these links working". but rather find out where the code is coming from, as it is not in our code base.
To try to eliminate the cause of the errors, as a first step I "temporarily" replaced the Google CDN library with a copy on our server on 29-Dec-11. The errors from the "strange foreign websites" immediately stopped and have not recurred.
I have only seen positive comments about using Google's CDN. After a bit longer time if the errors don't recur, I might re-enable the CDN to see if the errors start back up again.
My question: could these be coming from addons that users have installed on their browsers, or are they coming from Google?
I am already aware that cloudfront is an Amazon service. There are numerous such errors starting back on 26-Jun-11. There is a pattern in which typically a dozen or two such errors occur in a short time from, all from a single IP address. Then there is a large gap of time. This makes me wonder if it could be something that a user does on their browser to use some facility of Amazon for example. Is your team aware of anything like this?