A follower on Twitter stated that they had some fraudulent activity on their VISA card. When they contacted their bank, the bank asked "have you used TrialPay lately?" Of course the answer was yes. They believe the compromised information was possibly because of TrialPay.
We've not had issues with the 3x we've used TrialPay. In fairness, we also have a new bank and bank card now. The former one we used didn't have any fraud activity on it, and is now canceled since moving banks.
Another user on Twitter made a great suggestion. To activate an offer that's TrialPay on the Viggle OfferWall, they used a pre-paid card that had little or no money on it. Some of the offers would give you +200 just for connecting your card to an offer. You then got more points once you made X amount of purchase at a retailer. The Twitter user said he used a pre-paid card to avoid any possible fraud.
It's a great idea. Any sort of active and valid pre-paid MC or VISA card (or whatever other kind the offer asks for) would probably work. You could load the card with just enough cash to cover a pending purchase, get your Viggle points, and not have to fret about fraud. It's a good safeguard if you're worried about it.