Note that several modem manufacturers have added a caller ID feature into their products, protecting the corporate network by allowing remote-access calls only from a list of preauthorized telephone numbers. Caller ID modems are an acceptable means of authentication in a low-security environment but, as should be clear by now, spoofing caller ID is a relatively easy technique for computer intruders, and so should not be relied on for proving the caller's identity or location in a high-security setting.