Any individual or corporation who has price-sensitive information about a public corporation which is inaccessible or not available to the public and who uses that information to trade in stocks or bonds to his own benefit is guilty of insider trading. Inside trading flourishes best at a time, when there is a high proportion of takeovers and mergers, for those are the events which most effect share prices.
Until perhaps the 1960s in the UK, and 1930s in USA, insider dealing was not just legal; within limits it was perfectly acceptable. Gradually insider dealing came to be recognized for what it is: a form of theft. In the UK insider dealing was made a crime in 1980.
Insider trading scandals have recently involved Pechiney SA and Triangle Industries in France; County NatWest WoodMac Securities and Guinness in the UK; Drexel Burnham, the Chicago Mercantile Exchange and The Chicago Board of Trade, and the Butcher brothers banks in the US; Operadora de Bolsa in Mexico; and the Recruit Cosmos Co, Nippon Steel and Sankyo Seiki, the central bank in Taiwan, and Kyodo Shiryo in Japan. In China in 1994 insider dealing, involving party officials and local bureaucrats as well as companies was widespread and had proven difficult to control.