Smathers, from West Virginia, has worked for AOL since 1999. In May 2003, according to the criminal complaint, he managed to gain access to a confidential customer database by using another employee's ID code. The database contained details of customer postcodes, screen names and credit card types but not, stresses AOL, credit card numbers.
AOL has over 30 million subscribers worldwide. Each customer is issued with one or more screen names, or User IDs, which serve, among other things, as a portion of an e-mail address. The database comprised 92 million screen names.
Smathers sold the details to Sean Dunaway, 21, from Las Vegas, say the prosecutors. Dunaway, also charged, used the e-mail addresses to market his internet gambling business and then sold the original list on to other internet marketers for up to $52,000. He also sold an updated but smaller list for $32,000.
The complaint also includes a claim that Dunaway earned between £10,000 and £20,000 per day from his spam operation.
Both men were arrested on Wednesday. AOL issued a statement confirming that Smathers had been fired and adding: "We deeply regret what has taken place and are thoroughly reviewing and strengthening our internal procedures as a result of this investigation and arrest."