On its own, the type of information is not considered to be particularly sensitive. But security experts worry that big e-mail lists like this could be used as a stepping stone by phishers to create targeted attacks that then trick victims into disclosing more valuable information or installing malicious software.

Hackers have repeatedly gone after this information in the past. In recent weeks both and software vendor acknowledged that they'd been hacked and e-mail addresses and customer names were stolen. In Ashampoo's case, the company's customers were then sent fake order confirmation e-mails that looked like they came from PurelyGadgets, a U.K.-based online retailer. These files contained maliciously encoded pdf documents that could install malicious software on the victim's computer if opened, according to Ashampoo.

In a breach that could affect tens of millions, Sony said this week that someone had and stolen some personal information, possibly including credit card data.

Because it includes the addresses of thousands of season ticket holders, the spreadsheet could also give thieves a pretty reliable list of people to burglarize during Yankees games.

On the NYYFans.com discussion forum, fans were split -- some calling for the sales rep's job, others for forgiveness. "It's a big mistake, but it's still a mistake," . "To call for a man's job over this seems heartless."