That's not to say our POTS (plain old telephone service) is unbreakable. One of the legends of hacking is Cap'n Crunch, who got his nickname from decoding the audible signals on phones by using a whistle from a box of the cereal. The hackers who followed in his footsteps didn't break into POTS for the free long-distance service. They did so to access the computers connected to it. But they don't need POTS any longer; they've got the Internet now.
So users have been able to ring you up when their systems have crashed after someone let loose variants of the SoBig or Klez viruses on your network. But with VoIP, users might not even be able to do that, since its infrastructure is vulnerable to the same attacks by the world's bottomless pit of sociopathic hackers.
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