Hello
The text appears in two properties files:
1.) In coreMessages[en].properties within sap.com/tc.sec.ume.core~impl.jar (within the JAR under the path com\sap\security\core\util\resources); the JAR can be found under bin/ext/com.sap.security.core.sda/lib/private
2.) In LogonMessages[en].properties within sap.com/tc.sec.ume.core~impl.jar (within the JAR under the path com\sap\engine\services\security\exceptions); the JAR can be found under bin/services/security/lib/private
I don't know which of the both properties files really are taken into account, but that's easy to test now.
Cheers,
Tapan