A 21-year-old computer engineer has admitted hacking into a wireless network and accessing files on hundreds of its customers. Nicholas Lee Jacobsen pleaded guilty in Los Angeles federal court yesterday to a charge of felony hacking. He'll be sentenced in May and could get five years in prison and a quarter million-dollar fine. Prosecutors say Jacobsen had posted a notice online saying he could provide the names, Social Security numbers, birth dates and passwords of customers of T-Mobile USA. T-Mobile has more than 16 million customers but says Jacobsen was able to see information on only about 400 of them. And the company says he was not able to access credit-card numbers or other financial information. One of the customers was a Secret Service agent who helped track him down.