Brian Salcedo, 21, from Michigan admitted he was part of a gang that tried to steal data from Lowe's home improvement stores.
Salcedo and the gang are reported to have used wardriving on one of the stores in the Detroit area. The firm experienced losses of more than $2.5 million.
Salcedo has agreed to provide information to the authorities in the hope of a reduced sentence.
Fellow group members, Adam Botbyl (20) and Paul Timmins (23) are scheduled for trial later this month. Botbyl and Timmins were reported to be part of the 2600 hacker club in Michigan.
Hackers penetrated the wireless network, which was linked to stores in various US locations. The hackers left a tool to record customer information that they could pick up later.
The FBI followed and arrested the men after finding them wardriving in the company's car park.