Sophos Web Content Scanner and PCE Client causing slow IE performance.
If you are using Sophos AV software and PCE Client there may be a performance issue whilst using Internet Explorer. This is because the Sophos add-on checks the redirection function of PCE Client.
The redirection function is enabled when PCE picks up a banned website according to it's filter lists. The web page is blocked and PCE redirects the browser to your chosen redirection URL. This URL is specified in your PCE Console (System Options, Internet).
The Sophos add-on grabs that redirection request and checks it for verification. It is this check which can cause IE to hang.
If required you can disable the Sophos Web Content Scanner for all users via group Policy.
Please see the following Sophos knowledgebase article; http://www.sophos.com/support/knowledgebase/article/45206.html