VoIP hackers gut Caller ID
Wednesday, 7 July 2004 13:48 EST



Hackers have discovered that implementation quirks in Voice over IP make it easy to spoof Caller ID, and to unmask blocked numbers. They can make their phone calls appear to be from any number they want, and even pierce the veil of Caller ID blocking to unmask an anonymous phoner's unlisted number. At root, the issue is one of what happens to a nugget of authentication data when it leaves the tightly-regulated realm of traditional telephony, and passes into the unregulated domain of the Internet.

On the old-fashioned phone network, Caller ID works this way: your local phone company or cell phone carrier sends your "Calling Party Number" (CPN) with every call, like a return address on an envelope. Transmitted along with your CPN is a privacy flag that tells the telephone switch at the receiving end of the call whether or not to share your number with the recipient: if you have blocking on your line, the phone company you're dialing into knows your number, but won't share it with the person you're calling.

Read Full Story