Wired offers an in-depth look at how hackers crippled Ukraine’s power grid last year. Very interesting that they deployed TDoS attacks to flood the power company’s call centers so nobody could call in to report anything:
[…] they launched a telephone denial-of-service attack against customer call centers to prevent customers from calling in to report the outage. TDoS attacks are similar to DDoS attacks that send a flood of data to web servers. In this case, the center’s phone systems were flooded with thousands of bogus calls that appeared to come from Moscow, in order to prevent legitimate callers from getting through.
Most enterprises probably haven’t even thought about defending against TDoS attacks, but it’s definitely a threat these days with cheap VoIP and number spoofing. Not to mention cybercriminal call centers.