The head of Belgium's intelligence service has said Brussels is home to more spies than almost any other city.

EU countries have a protocol for sharing official "secrets." But motives for classifying files are not always pure and the number of really hush hush papers in Brussels is tiny.

EUobserver's list of 144 lobby firms in Brussels, with financial data where available.

Lobby firms are the "eyes and ears" of their clients, with the daily hunt for EU information worth up to 70 percent of their business.

Classified files can damage EU interests if they get into the wrong hands. But where is the line between security and transparency? What is the difference between a lobbyist and a spy? EUobserver investigates.

Andrew Rettman writes about foreign relations for EUobserver. He joined the site in 2005 and specialises in Israel, Russia, the EU foreign service and security issues. He is 37 years old and was born in Warsaw, Poland.