Also, the Anonymous people have made themselves a pain in the ass to governments who have the resources to find them. Even if the cartels don't have ears in the right place it's not hard for me to imagine a list of probable Anonymous members somehow making it into their hands.
Hey kid : People tell me you're the smartest computer guy in your year. My friends know where your mother lives. Please help me find some of these "hackers".
The Los Zetas cartel, being the second largest cartel in Mexico, probably has revenues of well over a billion dollars per year. (It's estimated that the overall earnings of all Mexican drug smugglers is $13-40 billion.)
I'm pretty sure that's enough money to hire a hacker or two.
As an aside, I don't know of any billion-dollar industry that doesn't have a fairly high level of sophistication. I don't see why the cartels should be any different.
Moreover, it is known that cartels have connections in every government agency, such as the CISEN (Mexico's national security agency), Policía Federal Ministerial (Mexico's FBI). That's one of the reasons why a lot of "protected witnesses" or people who report crimes are murdered, because there is always someone inside these agencies.