I use lightspeed for our content filter, they just sent me this warning about shortened url services and proxies. I thought I would share.
In recent months, we have seen an increase in the misuse of URL shortening/redirect services (e.g. Tinyurl.com, bit.ly, cli.gs). These services take lengthy URLs with descriptive attributes embedded by web developers and make the associated pages available through a shortened web address. Unfortunately, these services make it possible for users to access proxy servers and be exploited by spammers.
As a result, Lightspeed Systems is changing how URL shortening services are being categorized. Effective Monday, November 30, 2009, we will categorize these sites in the normally blocked Security category (see Master Category List on the Lightspeed Wiki).
If you need to use these services in your organization, you can continue to do so by placing them in an Allowed category--learn how.
As always, if you have any questions please contact us.
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Chief Operations Officer