Bottom line is that TT had a lot of data taken by one of their contractors last December. So the scammer already has a load of info.
Most scammers have quite a lot of information, the "Microsoft" scammers knew my details when they rang me. I played along with their scam in a virtual machine and I hung up when they asked me to load Paypal in a browser.
I then left the house, and when I came back I saw that they had tried to ring me literally dozens of times.
In the case of TalkTalk I believe the only extra piece of information gained was the account numbers. But then, I've never had a company verify their identity by reading back my account number.