If your Sophos users are experiencing slow browsing or your Smoothwall Filter and Firewall is demonstrating consistently high load average over a long period of time, you can add the Software Updates category to your authentication exceptions, see our help topic, Creating authentication exceptions.
Every time the client device makes a request, Sophos intercepts the request and sends a request of its own to Sophos' own servers. This is to check that the request is "safe" before being passed along to the default gateway or proxy. This effectively doubles, or sometimes triples, the number of requests made. This can have a serious impact on box performance. There are also no pop-ups or notifications to indicate when Sophos has blocked a page or component of a page from loading.
An example we have seen recently is where a web page wouldn't load properly. Upon switching off the Sophos Intelligent Web Service, the site began working correctly without any modifications being made to the Smoothwall Filter and Firewall's configuration. If you know Sophos is running on a client machine, it is recommend disabling it and testing again before contacting us for troubleshooting.
Additionally, Sophos doesn't support authentication requests so if you are running NTLM, requests will fail. This can contribute to slow browsing, high disk load and authentication service overload as the number of requests queuing can be very high as a result of the number of Sophos requests.