Pet supply retailer PetCo.com plugged a hole in its online storefront over the weekend that left as many as 500,000 credit card numbers open to anyone able to construct a specially-crafted URL.

The pet site was vulnerable to the same kind of SQL injection vulnerability that lead to an FTC complaint against the fashion label Guess, in a case that settled earlier this month.

Twenty-year old programmer Jeremiah Jacks discovered both holes. Jacks say news media interest in the Guess case prompted him to check a few other large e-commerce sites for similar bugs. He chose PetCo.com because a competing e-tailer had been vulnerable last year, "so I was wondering about other pet sites," says Jacks.

Jacks used Google to find active server pages on PetCo.com that accepted customer input, then simply tried inputting SQL database queries into them. "It took me less than a minute to find a page that was vulnerable," says Jacks. "Any SQL injection hacker would be able to do the same thing."

He says the database contained 500,000 credit card entries, and that he could have accessed corresponding customer names and address, as well as entire orders. "Everything was in there... It exposed their whole database," says Jacks.

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