T-Mobile is the fourth-biggest wireless phone provider in the United States and in the United Kingdom. Recently, however, the company is suffering a string of public relations fiascoes. In the United States, there was the situation in which Sidekick phone users found that their information went missing — it didn’t matter to a lot of people that the hardware on which the data was stored wasn’t owned by T-Mobile, it just mattered that their Sidekicks were T-Mobile phones.

Then the wireless carrier’s network went out. Earlier this month, as Ina Fried wrote, lots of people (myself included) found themselves unable to make calls on their T-Mobile phones on November 3 because of a network outage.

Now from the United Kingdom comes news that a T-Mobile employee allegedly sold personal information on thousands of customers to third parties, according to the BBC and the Guardian. Richard Wray of the Guardian said the data breach was the biggest of its kind to date, affecting thousands of customers and millions of individual records. T-Mobile itself reported its suspicions that something had happened to the authorities. The company claims that it had no knowledge of the employee selling information until after it happened. I wouldn’t be surprised if that’s true, but it’s still going to leave T-Mobile with a couple of black eyes and a whole heap of ill will from its customers in the United Kingdom and possibly other countries where this news is breaking.

How did we know it happened? Suddenly people whose contracts with T-Mobile were expiring were getting sales calls from telephone providers asking them to sign up for a new contract or to switch networks. The U.K. Information Commissioner’s Office announced the data breach publicly, and one by one, the other U.K. wireless providers came forward to say they weren’t the affected networks. As a result, T-Mobile was forced to confirm its employee was the alleged source of the breach.  A spokesperson said the company had been asked to keep quiet to prevent any affect on the criminal trial.

The BBC said the Information Commissioner’s Office has interviewed T-Mobile employees and is accessing company property with a warrant as part of the investigation. The identity theft includes names, addresses, phone numbers and the date of expiration for their phone contracts, according to Wray’s article. Call records and financial information weren’t sold. Still, that’s cold comfort for the approximately 16.6 million customers the company has in the United Kingdom.

For more on wireless phone networks and data theft, take a look at these articles on HowStuffWorks.com:

How Cell Phones Work
How to Protect Against Identity Theft
How Identity Theft Works