Oprah Winfrey has been accused of employing dirty tactics in an attempt to prevent her company Harpo Productions from becoming the subject of a revealing expose, according to reports. Keifer Bonvillain - who calls himself a "civil-rights activist" - is courting a number of publishers to get backing for his book Ruthless, and has launched a website to attract potential investors. Bonvillain, 37, was arrested and charged with federal extortion last year (06) after trying to sell Winfrey audiotapes of a prominent Harpo employee criticising her for $1.5 million (GBP750,000). But the charge was thrown out of an Illinois court. And Bonvillain claims he became the victim of a robbery when he announced he was to use the tapes to pen a revealing book about Winfrey's TV company - because the U.S. chatshow queen wants to keep her business practices hidden from the public, reports the New York Post's gossip column Page Six. In his pitch for the tome, Bonvillain says, "An office manager at Harpo broke his silence and his confidentiality agreement when he spoke freely about Oprah Winfrey's private life and business affairs. "Keifer Bonvillain underestimated one of the world's most powerful women when he, armed with clandestinely recorded tapes, decided to write a 'tell-all' book unmasking the famed celebrity. Within days of Harpo learning about the book, two men were attempting to break into Keifer's home - presumably to get the tapes. Oprah was desperate to keep the truth from being revealed... The fallout was Keifer's highly publicised arrest." He also claims the company has been involved in "blatant discrimination... This CEO (Winfrey) not only knows about these practices... she condones them... Hours of taped conversations... reveal what they don't want the public to know about (Winfrey's) private life, and a business that prides itself on its diversity." This is the latest controversy Winfrey has been faced with in recent weeks - last month (Oct07), the TV mogul was forced to issue a statement regarding accusations of child abuse at her South African all-girls school, Henley-On-Klip Leadership Academy. Former dorm matron Virginia Mokgobo, 27, was arrested on 29 October (07) on numerous charges, including assault, indecent assault and soliciting underage girls to perform indecent acts. A total of 15 victims have since come forward. Mokgobo has been bailed pending further investigation.