Numbered bank accounts are a well-known Swiss institution. These accounts are identified only by a number, assuring the account holder anonymity. Naturally anonymity brings the risk of attracting funds of dubious origin, or money that is simply trying to avoid the attention of tax inspectors.

Numbered accounts were introduced in WW II, allegedly to provide cover for funds escaping from Nazi control. Since then Swiss banks have been a favourite destination for funds spirited away by corrupt figures - President Mobutu of Zaire, for example, is estimated to have US$8 billion squirrelled away in Swiss banks.

Perfectly legitimate money flows in too, of course, attracted by the stability of the country. In 1990 a law was passed forcing the banks to identify the owner of monies deposited in the event of an investigation. The legislation was inspired by the arrest in Switzerland in 1988 of two drug traffickers who deposited Sfr1.5 billion in a Zurich bank. The deposit attracted attention because it was marginally higher than the average Swiss salary cheque.