The Committee to Nuke Elysium

the very factors that have brought Facebook and similar sites such commercial success have huge appeal for a secret police force. A dissident’s social networking and Twitter feed is a handy guide to his political views, his career, his personal habits and his network of like-thinking allies, friends and family. A cybersurfing policeman can compile a dossier on a regime opponent without the trouble of the street surveillance and telephone tapping required in a pre-Net world.

If Mr. Mubarak’s Egypt has resorted to the traditional blunt instrument against dissent in a crisis — cutting off communications altogether — other countries have shown greater sophistication. In Belarus, officers of the K.G.B. — the secret police agency has preserved its Soviet-era name — now routinely quote activists’ comments on Facebook and other sites during interrogations, said Alexander Lukashuk, director of the Belarus service of Radio Free Europe/Radio Liberty. Last month, he said, investigators appearing at the apartment of a Belarusian photojournalist mocked her by declaring that since she had written online that they usually conducted their searches at night, they had decided to come in the morning.

In Syria, “Facebook is a great database for the government now,” said Ahed al-Hindi, a Syrian activist who was arrested at an Internet cafe in Damascus in 2006 and left his country after being released from jail. Mr. Hindi, now with the United States-based group CyberDissidents.org, said he believes that Facebook is doing more good than harm, helping activists form virtual organizations that could never survive if they met face to face. But users must be aware that they are speaking to their oppressors as well as their friends, he said.