Federal court officials in northern Illinois are warning residents about a nationwide scam involving fake arrest warrants.  People have been contacted by phone, email and fax by individuals claiming to be law enforcement officials and demanding money to throw out supposed arrest warrants for offenses such as missed jury duty, money laundering and bank fraud.  The U.S. District Court in Chicago said in a news release Saturday that some offenders have asked people for personal identifying information, money orders and prepaid cards to cancel bench warrants.  The news release emphasizes that valid arrest warrants are always served in person by a U.S. marshal or other law enforcement officer and not by phone, email or fax.  Anyone receiving a suspicious call or email is asked to contact the U.S. Marshals Service.