Well, I just had my debit card number stolen online and used to the tune of $850 in charges. Even though it says 'VISA' on mine, I found out that the safeguards built into credit card purchases are NOT there for debit cards. If it was a credit card, I would likely get my money back. As it is, it depends on whether the vendors involved will pay me back out of the kindness of their hearts.
I mention this here because the only possible source of the theft is one of three online magic vendors I made purchases from shortly before the fraud. Before these purchases, it had been a couple of months since I'd last made an online purchase using my debit card, so the odds are very good the breach came from one of these vendors.
I have notified these vendors, and expect they will be very helpful. Odds are good that one of them has a security breach in their purchase system that a hacker is exploiting, or has a dishonest employee who simply stole my information.
I have cancelled my debit card, and from now on will only be using a credit card for online purchases. I figured the least I could do is share my experience here so you all could benefit from my mistake.

Airship, Sorry to hear about this happening to you. Unfortuneatly the public and a lot of sellers on line have been misinformed about security on internet purchasing. Every one has been told that you cant break 128 bit encryption. That is not true. They say that it will take 4 weeks straight on a supercomputer to break it. That is not true either. When I was going to college for computer programming one of our assignments was the attempt to break 128 bit encryption. Me and 2 others were able to crack it. It did help that we were also very expeirienced at cracking things though. Now let me just go on to say that I never hacked any thing for destruction. Just for learning. Good crackers are the ones that do a majority of the damage. It is unfortunate that are cards are not safe any where. But using your card on the internet is a lot safer than using it over the phone. Phreakers are still at large. I worked at a call center for toys and we had to deal with phreakers all the time getting card numbers by phreaking our phones. Back onto topic. If your bank allows you to use your debit card as a credit card, then they should have a card center. You will have to fill out a dispute file. But most all debits from banks can be disputed and your losses recovered by the bank. Some banks don't want you to know this, Because it actually causes them to have to work. But don't be fooled by them. After 4 years in the banking industry there are lots of things the banks can do that they just don't want people to know about.

Thanks, Corey. I pressed my bank and found out my losses will probably be covered by VISA, though the SOBs at my bank sure didn't want me to know it.
I know quite a bit about internet security myself, which is what makes this particularly embarrassing. But the problem is that any system can't be made 100% safe. I strongly suspect a dishonest employee is probably the weak link, but who knows?

Airship, I am glad to hear that visa is going to be taking care of things. Like I said, Banks don't want you to know that kind of thing. You are probally right about an employee getting the numbers. It can really be a waste for a cracker to sit online and try to catch card numbers. But we may never know for sure.

I've had two credit cards stolen in recent months. There is a way to find out who stole the information. Here's the way you do it.

Call the store where the order was placed, and tell them who you are, your old credit card number (you did cancel it, didn't you?) and explain that they have been victimized by a thief. Ask for the address that the item was sent to. Also, get the name they used. The DA in that town will be happy to help.

Here's what happened to me. I was on my way back from a convention in February, and I spent the night in a motel in McKinney, TX. I put it on my Amex card. I use my Amex card ONLY for travel purchases, even on line. When we got our Amex bill, I found two bogus charges on it, so I called the people who had gotten the charges, and asked where the stuff was sent. They gave me a name of a person in McKinney, TX. I called the motel -- part of a MAJOR chain, and they told me that the employee who had printed my card had been the thief. She had sent all the merchandise back, so I wasn't charged. But I cancelled the card and had a new one issued.

Once the charge goes off your debit card, change banks.

Here's something else to watch for. Aways check your statements. If you see a charge that comes up and is then cancelled, and you don't know anything about it, cancel the card. The person who made the charge is "testing the water." They will get you later.