Bierman, D.J., (1991) A method to fraudulently produce effects in a conceptual replication of the Schmidt-Morris-Rudolph retro-PK by the SRU (Eindhoven) and the Dutch sceptical community (Skepsis) was communicated by letter of May 17, 1991 to R. Nanninga of Skepsis. The method was based upon a date-sensitive computer virus.