Tradition, all the Russian/CIS carders have always used jabber or ICQ mainly because they aren't worried about being caught and don't care about the security of their customers either. The bigger fraud outfits like Rescator are likely politically protected being a nephew to a cabinet minister or son of a Novosibirsk police captain. If you are a non connected Russian and try to run a fraud superstore the US feds can bribe lower level police agencies there to go make your life hell.
Your first sentence insinuates that Jabber is insecure. Could you elaborate on that? Just genuinely curious, since I used jabber/otr for a while to communicate with friends.
They seldom use OTR, I think infraud (in fraud we trust) still uses a group server in Azerbaijan to cleartext chat on none of these guys really care, some of the boards still use cloudflare.
Icq is very popular on some countries, for example Russia.
There is a interesting phenomenon with IMs in that they tend to have popularity based on geographical locations and language borders, despite being on Internet.
Examples: in russia Icq is king. Brazil had Icq until MSN Messenger showed up, Icq tried and failed to get it back, gave up, then Microsoft became stupid and closed MSN Messenger, now the leader is Facebook messaging and whatsapp. Last I checked in us people used aim and yahoo clients.
Gmail messenger was a popular second place in many countries until Google killed it in favour of hangouts, now for text people use Facebook and for video they use Skype, that was, and kept their leading position.
In China the thing is Baidu client.
In Africa there is some messenger clients tied to local isps and phone companies.