Dark Angel by John Sandford

Letty Davenport’s days working a desk job at are behind her. Her previous actions at a gunfight in Texas—and her incredible skills with firearms—draw the attention of several branches of the US government, and make her a perfect fit for even more dangerous work. The Department of Homeland Security and the NSA have tasked her with infiltrating a hacker group, known only as Ordinary People, that is intent on wreaking havoc. Letty and her reluctant partner from the NSA pose as free-spirited programmers for hire and embark on a cross country road trip to the group’s California headquarters.

While the two work to make inroads with Ordinary People and uncover their plans, they begin to suspect that the hackers are not their only enemy. Someone within their own circle may have betrayed them, and has ulterior motives that place their mission—and their lives—in grave danger.