(I got an ARC through NetGalley, in exchange for an honest review.)
3.5 stars, because the book wasn't without faults. In fact, I'd probably give it 4 stars in other circumstances—that is, if I didn't know a lot to the online world, computers in general, and hackers. Some parts I found to be too "didactic", which would be good for a reader with a less technological background, yet tended to become annoying after a while (I really don't need to be taught what a DDoS attack is). However, this is a "it's not you, it's me" kind of fault, and I don't doubt it's precisely what would help another person enjoy the story more.
The events in the last third of the book also seemed to move just a tad bit too fast, making things somewhat confusing. I guess I would have liked to see more hide and seek there? Or a different approach? It's actually hard to tell. I just know that I went "huh?" in a couple of places.
I liked the main characters, the ways they went through to meeting, and how they generally thought of clever little tricks to avoid being noticed (how to trick facial recognition software, etc.). Perhaps their relationship was a little forced, but it didn't matter that much within the flow of the story.
The reflections the book leads to when it comes to social media and their impact on our lives, were interesting as well. So many people use their real names on such media, handing out very specific information, without realising that it could be exploited. Reminding this to younger readers (middle-schoolers, the "YA crowd"...) is certainly not a bad idea at all. Anyway, the use of social media, through the giant "Panjea", was both a reminder and a wink, and I appreciate that kind of things.
Overall, it was a light, fast-paced read that could be quite enjoyable for a lot of readers. Had I been "younger" (less experienced, with less computer/online knowledge than I have now), I'd probably have given it 4 stars.