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It started with thousands of "(direct) / (none)" inbound visits showing in Google Analytics.

A close look at the server log file found many lines with truncated referrer information coming from an ad server.

Our ad agency is using an adserver to display flash ads on many sites which bring the visitors to our site.

Here is good referrer information from a log file line

Here is a truncated information from a log file line

My question: What causes the referrer information to get truncated in the log file?

Is this the fault of the ad server? Is it sending http headers with truncated referrer information?

Is this the fault of my web server that in many cases writes the line with truncated referrer information?


Following the information in DerfK's answer, I have checked the User Agent information in the log file and found that the all the truncated referrer visits was by visitors that uses IE, all versions.

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up vote 1 down vote accepted

The Referer header comes from the browser, not from a server, so it's not the ad server's fault. Since your server appears capable of logging longer Referer headers, its not your server's fault.

That leaves the browser. It would probably be educational to have the server log the User Agent string and compare the ones with truncated headers to the ones without.

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Thanks! That was really helpful. The common factor is (drum roll please...) MSIE! 6.0, 7.0 , 8.0, 9.0 – Hanan Cohen Aug 13 '12 at 7:27

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