Thanks GoodGuy. All good advice. I have already ran full system scans with ESET and Malwarebytes. My credit card's been stopped by the bank, so it won't matter now. But I don't leave CC details on sites I purchase from anyway. But I will change my password on Dell. Thanks.
Use Trendmicro's free online scanner (if it's still up) and see if it finds anything. A local scanner and an external scanner, that's the best combo. Just don't let it clean (the cleaner can be harsh) anything if it finds something, they have removal instructions.