public SecurityChallenge getDefaultSecurityChallenge(String username) {
		
		for(LdapServer ldapServer : ldapServers) {
			try {
				SecurityChallenge challenge = ldapServer.getDefaultSecurityChallenge(username);
				if(logger.isDebugEnabled()) {
					if(challenge != null) {
						logger.debug("Successfully got default security challenge for " + username + " at " + ldapServer.getDescription());
					} else {
						logger.debug("Got null default security challenge for " + username + " at " + ldapServer.getDescription());
					}
				}
				return challenge;
			} catch(NameNotFoundException ex) {
				logger.debug("Didn't find " + username + " in " + ldapServer.getDescription());
				// ignore... we'll try another server
			} catch(ObjectRetrievalException ex) {
				logger.debug("Multiple results found for " + username);
				// ignore it... try the next server
			}
		}
		
		logger.debug("Couldn't find default security questions for " + username);
		throw new NameNotFoundException("Couldn't find username " 
				+ username + " in any of provided servers.");
	}