Ch. 2: Hacker
When Wesley was trying to dump more energy into the food replicator to try and recreate one of the exotic dishes Q had brought him from some star system never explored by humans, someone else on the Enterprise blocked him. He later caught this 'someone else' hacking into the holodeck program, trying to create an untraceable memory circuit and he blocked him. And thus began a mini-hacker war. He figured out it was Lieutenant Barclay pretty quickly and first called him "Broccoli" during one of their late-night hacker wars. He knew Barclay would never say anything since Barclay was doing things he shouldn't have been doing either. He eventually found a way to hack into the ship's systems without Barclay knowing, but it was a real hassle there for awhile. Barclay had been good.
He figured out how to hack into Data when he was 13. He didn't want anything like Lore to try to take Data's place again. The first time Data "felt" anger was actually his doing. He was pissed off that Kivas Fajo had stolen Data and he tapped into Data's aggression program designed for self-defense and triggered it, bypassing his ethical programming. He had still been getting signals on his computer console in his quarters that Data was still alive but he couldn't very well tell everyone on the ship that he hacked into a superior officer. He thought he would have to play the sympathy card and remind everyone of Data and his accomplishments to get them to investigate properly but to his luck, La Forge had already been worried enough. When Fajo's ship was back in range, he was able to properly send signals to Data again. After that incident, he knew he had to create a more long-distance systems connection to Data. The new connection he created allowed him to keep tabs on the Enterprise even while he was at the Academy.
He heard later from Commander Riker that Data had told him something must have happened during transport when an outlawed weapon in his hand was detected as being fired, which led him to believe he must have confused Data's systems enough when he was hacking into his aggression programming that Data honestly didn't know what had happened at the time. Data hadn't been trying to lie to Commander Riker. Wesley felt guilty about Data's seemingly hazy memories of the few seconds he hacked into his systems. It made it clear that Dr. Soong never wanted to create a soldier.