Target: Up to 40 million cards compromised

Target says a breach of credit and debit card data may have affected as many as 40 million shoppers who went to the store in the three weeks after Thanksgiving.

Target: 40 million credit cards compromised

The hackers targeted the systems at Target's brick-and-mortar stores, not the website.

OutFront: David Kennedy is CEO of TrustedSec and is a "white hat hacker" who looks for security flaws.