More on the credit card fraud

The fraudulent orders that I receive on my site come with email addresses of eight random alphanumerics @yahoo.com. Is anyone handy enough with regex or can show me a quick way to test for that, so I can at least refuse all orders with that pattern? (it will work for a little while, until they get wise and change patterns again.) Many thanks, - Brian PS - If anyone wants an update: the orders stopped for a while but started up this weekend with a vengeance. Now they are coming with valid address verification AND card validation numbers! Pretty darn good, whoever's doing it. One of the cops I've spoken with says that they're making a large number of small charges (like mine) to these cards and then, in one case, placing a large $2000 order from QVC. In that case the large charge was declined, thankfully.