This bears repeating because its an unfortunate ploy of recruiters. They mine the public for information about jobs. They may not be calling you up because they have a job in mind for you. They may be calling to pick your brain and ask you names and phone numbers of your previous supervisors and co workers to use as “warm leads”. Sometimes that will be the first thing they ask when they call you or email you. “I need your references before we go any further”. After you give them your references, you may never hear from them again. Don't agree to give out references until after you have a first job interview.