"Deep-packet inspection is the one of the most invasive things a country can do to its internet. Employed by repressive regimes from Russia to Bahrain, it lets governments look into the content of web traffic as it moves over the network, allowing them to censor websites in real time and conduct detailed surveillance of citizen's activities on the web. They also require sophisticated equipment, usually provided by a western company. As a result, DPI installations are usually kept secret for as long as possible."