Intruder

I quite like this one; in particular, there's a page that makes the hair on the back of my neck stand up. That's a good thriller! It's from the early computer era (1979), a detective story with strong psychological thriller elements. A town that runs everything with computers finds itself held hostage by a hacker; the detective must find the intruder before more lives are lost. I picked up the ebook of it for $2.99, even though it's over 300 pages long. And of course you should be able to get it through your library, although they may have to resort to interlibrary loan. In it’s time it was near-future science fiction, but now it’s just regular fiction. It’s still good though.