G4S plc (formerly Group 4 Securicor) is a British multinational security services company headquartered in central London It is the world's largest security company measured by revenues and has operations in around 125 countries. With over 620,000 employees, it is world's second largest private employer, and the largest on the London Stock Exchange. G4S was founded in 2004 by the merger of the UK-based Securicor plc with the Denmark-based Group 4 Falck.