I got hit with this one:

Altavista Web Desighn L Tel 7572716046 $9.95

I called my credit card company (citibank) and they immediately removed the charge.

FYI:
A few months back I was charged by ESTOREONLINE too. This was on my AMEX Blue card that I NEVER use. Luckily the amount was in $20 range, but since I never use the card, I notice it immediately and complained to AMEX. They investigated it for a few days and finally closed the case in my favor. I was wondering the same thing as many of you are, as to how these charges turned up in the first place!

I tried to find out how my debit account was charged. The bank that let the money go (Bankone - now Chase) wouldn't talk to me, but a friend in the banking industry explained that the merchant is supposed to do the verification (you know, name, your card's CVV, expiration date, etc). Now, when the merchant contacts the bank for your money, there is NO VERIFICATION REQUIREMENT whatsoever - they just pull whatever money off of the account they are given the number of.

That kind of freaked me out... Can anyone confirm/deny this through your sources?

I didn't read every single post in this thread so it's possible this has been brought up, but here's another way your number may have been "compromised":

Your 16 digit Visa/MC number is not random. The first digit determines Visa(4) or MC(5), the next few determine bank, card class, etc with the last digit being a check digit based on a very simple formula. I won't go over the exact formula (you should be able to Google it if you're that interested), but one of the effects of this is that it's easy to generate another valid CC# from an existing one by adding 8 (or 18 if the digit in the "tens" column wouldn't change) to it. For example (last 4) 8523 -> 8531 -> 8549 -> 8557 -> etc
This used to be somewhat sensitive information, but since nowadays being able to generate another valid number (while most businesses now requiring address, zip code, and CVS) is rather useless I'm not as concerned about giving it out. However, it's entirely possible that people are signing up for fake merchant accounts (or otherwise gaining access to legitimate ones) and authorizing tons of transactions to random card numbers they've generated using a technique like this (without "verifying" the cards since the verification is really more of a service to the merchant as they're the ones who usually lose out when charges are disputed). There's a good chance some percentage of these charges won't be contested and in the end they'll make a few bucks doing it. This may or may not be what's going on with some of these fraudelant charges!