It appears that the compromised account is no longer used and the company is investigating the extent of the leak. CEO Lowell McAdam released a statement that included:

"This week we learned that a number of Verizon Wireless employees have, without authorization, accessed and viewed President-Elect Barack Obama's personal cell phone account. The account has been inactive for several months. The device on the account was a simple voice flip-phone, not a BlackBerry or other smartphone designed for e-mail or other data services.

"All employees who have accessed the account - whether authorized or not - have been put on immediate leave, with pay. As the circumstances of each individual employee's access to the account are determined, the company will take appropriate actions. Employees with legitimate business needs for access will be returned to their positions, while employees who have accessed the account improperly and without legitimate business justification will face appropriate disciplinary action.

Even if no current data was leaked and the information was only shared between company employees this is a black eye for Verizon Wireless. In Verizon Wireless' favor, they seem to have detected the problem, reported it to the Obama transition team and took immediate action internally.

When prevention fails, detection is the next best defense. Here is a case where the response to a data leak may be one of the best methods for preventing further leaks. The keys are how much detail will the investigation uncover and what disciplinary measures will be used.

Insider data leaks are a well known problem, see here and here.