Last week, Epsilon was a little-known e-mail marketing firm, a behind-the-scenes player in the Web-marketing world. This week, it's held a prominent place in the headlines as the target of a massive data breach that exposed names and e-mail addresses for a broad swath of customers at dozens of prominent companies.

E-mails from the likes of Citibank, Chase, Capital One, American Express, Walgreens, Target, Best Buy, TiVo, TD Ameritrade, Verizon, and Ritz Carlton--have been flooding in-boxes since Epsilon announced its system had been breached. Some people (this writer included) have reported receiving as many as four of these warnings.