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Why no compression?<br><br>We have found that there are 4 major reasons why users do not get compressed content: anti-virus software, browser bugs, web proxies, and misconfigured web servers. The first three modify the web request so that the web server does not know that the browser can uncompress content. Specifically, they remove or mangle the Accept-Encoding header that is normally sent with every request.<br><br>Anti-virus software may try to minimize CPU operations by intercepting and altering requests so that web servers send back uncompressed content. But if the CPU is not the bottleneck, the software is not doing users any favors. Some popular antivirus programs interfere with compression. Users can check if their anti-virus software is interfering with compression by visiting the browser compression test page at Browserscope.org.<br><br>By default Internet Explorer 6 downgrades to HTTP/1.0 when behind a proxy, and as a result does not send the Accept-Encoding request header. The table below, generated from Google's web search logs, shows that IE 6 represents 36% of all search results that are sent without compression. This number is far higher than the percentage of people using IE 6. <br><br>What should I do?<br><br>To reduce uncompressed content, we all need to work together.<br><br>    Corporate IT departments and individual users can upgrade their browsers, especially if they are using IE 6 with a proxy. Using the latest version of Firefox, Internet Explorer, Opera, Safari, or [http://google.com Google] Chrome will increase the chances of getting compressed content. A recent editorial in IEEE Spectrum lists additional reasons - besides compression - for upgrading from IE6.<br>    Anti-virus software vendors can start handling compression properly and would need to stop removing or mangling the Accept-Encoding header in upcoming releases of their software.<br>    ISPs that use an HTTP proxy which strips or mangles the Accept-Encoding header can upgrade, reconfigure or install a better proxy which doesn't prevent their users from getting compressed content.<br>    Webmasters can use Page Speed (or other similar tools) to check that the content of their pages is compressed.