Microsoft chairman Bill Gates has called for a law outlining how US internet companies should respond to censorship in foreign countries in wake of criticism of the firm's business practices in China. Speaking to the Financial Times, Gates argued that the internet was a tool for openness that would ultimately overcome any official censorship. His comments came as major US internet companies such as Yahoo and Google faced congressional hearings over alleged collusion with Beijing over censorship. They say defying the Chinese authorities would cut off access to their most promising market. Meanwhile official Chinese sources said that no one had ever been arrested for simply expressing an opinion on the internet.