More than 1,000 Mafia members have been indicted or imprisoned since the 1980's, and the entire governing commission has been convicted. Nonetheless, the Mafia is still very active in the United States and members regularly commit violent acts. The Federal Bureau of Investigation (FBI) reports the Mafia still represents the most serious organized crime problem in the country. Further, FBI field officers indicate Federal prosecutions have had little impact on overall Mafia activity. Nationwide, the organization remains particularly strong in Chicago, New England, Southern Florida, Las Vegas, Atlantic City, and New York City. The Sicilian Mafia may become a greater menace than its American counterpart. It appears to be rapidly "colonizing" the American underworld, and it members arrive in the United States legally since visas are no longer required for Italian nationals. As of 1992, the FBI estimated the Sicilian Mafia had between 10,000 and 20,000 members and associates. Involvement of the Sicilian Mafia in drugs and violence, particularly heroin, is discussed, and the dominance of the Sicilian Mafia in Philadelphia is considered.