I'm undertaking an audit of the cookies we use on our external sites.

There's one cookie that's used by all the sites, and by different domains within the sites. It starts BCSI-CS- and has random numbers and letters.

It's the same cookie on different PCs on our network. Our own sites use it and Bing Maps, Google Analytics and Google Maps on our sites use it.

This cookie does not seem to appear on PCs not on our network. We've figured that it's a cookie that our proxy server uses and therefore only an internal cookie, not one that our external site users will encounter.

However, googling that cookie shows a lot of sites have listed a similar cookie in their "About our cookies" page with the same BCSI-CS prefix.

Would we be right in thinking that these sites have got it wrong, that they don't have to list this cookie? After all, when I visit these sites, the cookie that they have listed does not appear on my PC.

Can anyone confirm this, or explain what the BCSI-CS cookie actually is?

2 Answers 2


The BCSI-CS-**** cookie is set by the Blue Coat proxy servers. It's not set by the website being visited, but as a result of accessing the site through a network (like a company network) using Blue Coat technology.

See also https://cookiepedia.co.uk/cookies/BCSI-CS-xxxxxxxxxxx and (for negative implications) https://www.ietf.org/mail-archive/web/http-state/current/msg01179.html


In my experience that cookie is used for tracking bounce rates, Web Trends use it for that exact purpose.

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