What is a proxy server, and what can it do? Mainly, a proxy server is a purpose built application that filters how your end user machines access the web. There are a couple different ways a proxy server can filter and regulate data flow from inside your network to the outside world. For those who may not know the technical details, a proxy server sits inside your network or service net, has access to the internet and also is connectable to internal computers. It then acts as a go between for your internal computers to get outside the network.
The first type of filtration from this sort of proxy server setup is content filtering. Basically, a proxy server sniffs all tcp traffic that transverses it and can block undesirable web sites, manually forbidden sites and even keywords to prevent employees from either intentionally or accidentally viewing offensive or harmful web sites. This is in keeping with most corporate policies and setups.
The second type is for a security measure. The nature of a proxy server is that it is protective of the boxes that utilize it. Which is to say, no one accessing the internet actually comes into contact with it at all, thus isolating them from view and vulnerability. It is analogous to sending someone else to deliver a message for you. You never have to leave your house, and they come into contact with the party you are communicating with on your behalf.
This protection from both security and liability perspectives makes a proxy setup popular among companies who do not wish to utilize a filtration appliance. It is a time tested, proven method to monitor, regulate and protect internal systems from exposure and attack from outside internet sources, and in concert with a modern, updated firewall device is a great compliment to any secure network configuration.