As a novice CIA case officer in the Middle East, Andrew Warren quickly learned the value of sex in recruiting spies. Colleagues say that he made an early habit of taking informants to strip clubs, and that he later began arranging out-of-town visits to brothels for his best recruits. Often Warren would travel with them, according to two colleagues who worked with him for years. His methods earned him promotions and notoriety over a lengthy career, until Warren, 41, became ensnared in a sex scandal. Two Algerian women have accused the Virginia native of drugging and sexually assaulting them, and, in one instance, videotaping the encounter. The episode -- one of three sex-related scandals to shake the CIA this year -- has drawn harsh questions from Congress about whether the agency adequately polices its far-flung workforce or takes sufficient steps to root out corrupt behavior. Former officers say the cases underscore a perennial challenge: guarding against scandal in a workforce -- the size of which is classified but is generally estimated to be 20,000 -- that prides itself on secrecy and deception. You have an organization of professional liars," said Tyler Drumheller, who oversaw hundreds of officers as chief of the agency's European division. Experienced field managers are needed, he said, because inevitably "some people will try to take advantage of the system . . . and it's a system that can be taken advantage of." The recent string of embarrassing revelations started with the CIA's former No. 3 officer, Kyle "Dusty" Foggo, who was indicted on corruption charges two years ago.