Remember when Target (NYSE:TGT) said that data from 40 million customers had been lost in a massive card reader breach? Well, good news -- now it looks like it's 70 million customers. Wait, that's not good news at all. Luckily, in the exact same press release where it announced the increase in the number of breached accounts, Target also announced a drop in its fourth-quarter forecast. Oh. That's also not good.

Target's bad news
While 70 million compromised "names, mailing addresses, phone numbers or email addresses" may seem like a bad thing, some analysts believe this is still just the beginning. As the number grows, Target customers are becoming more wary of the store. In its revised fourth-quarter outlook, the retailer cited decreased sales since the announcement of the theft.

For consumers, the news is bordering on horrific. The 70 million affected individuals means that the breach is already directly affecting more than 20% of the entire U.S. population. Target has expanded its credit monitoring program, now extending free monitoring and identity protection to all Target customers for a year. The program is supposed to be launching next week, with more details being released on Target's site as they're available.

What shoppers do to protect themselves
There are two scenarios for consumers: Either you were affected by this theft or you'll be affected in the future by another. If you're in the first camp, you can follow up with Target once its protection program goes into effect. That should help with some of the more subversive sorts of thefts that can come along. To simply protect your card, you can go to your bank or card provider and request a new card. That's a hassle, but it's less of a hassle than changing your cards after they've been used.

If you haven't been affected -- yet -- you can learn a valuable lesson here: Even the biggest companies are vulnerable. That means stores, banks, online retailers, and restaurants are also potential Targets. (Ha.) That's not to say that consumers should be scared -- just safe.

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Fool contributor Andrew Marder has no position in any stocks mentioned, and neither does The Motley Fool. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.