"Transparent proxies allow organizations to influence and
monitor the traffic from its users without their knowledge or
participation. Transparent proxies act as intermediaries between a
user and end destination, and aren't generally apparent to users
sitting behind them. Enterprises, Hotels, and Internet Service
Providers often use transparent proxy products to lower bandwidth
consumption,speed up page loads for their users, and for monitoring
and filtering of web surfing. When certain transparent proxy
architectures are in use an attacker can achieve a partial Same
Origin Policy Bypass resulting in access to any host reachable by
the proxy via the use of client plug-in technologies (such as
Flash, Applets, etc) with socket capabilities."