I trust licensed poker rooms and do not suspect them about anything particularly malicious, but one needs to be careful with anything online.
Hackers are one issue, but I am more afraid about the collusion of any type.
You can read the story about a former Amazon worker, who got upset and leaked thousands of customers credit card details.
Let us hope that
pokerstars pays their employees good enough not to be tempted with similar ideas.
As myself I use different passwords for different sites
have few emails , one for the friends, one for business, one for online payments etc.
My card is not connected with my main bank account but with the current account that has a limited amount of money in it.
The same is with
paypal I would not store a large amount of money there but supply the account with the money only shortly before needed transaction.