They do not use CableCARD; none of the DCT-series devices do. Only DCH-series Moto cable STBs do. If you are (as I suspect) considering buying one on eBay instead of renting from your cable MSO, they still won't accept a DCH-series box, as they're not on the CableCARD certified devices list (because they're intended for sale/installation directly by the MSO, not by an end user).
Edit: As for what they do use, they use integrated security services, which were restricted with the advent of the FCC's July 2007 CableCARD mandate.
Not prohibited, because the cablecos themselves use them, but if you have one that you acquired by any means other than renting it from your MSO, they're not going to touch it with a ten foot pole. If you seriously suggest you want to use it, expect a response along the lines of someone watching as your face turns inside out.
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