They call this "wardriving" (cf "wardialing" by hackers looking systematicaly for modems on landlines back in BBS days). Like wardialing in the old days, there is more wardriving going on today than most people think and you won't know they are doing this like with wardialing because at least back then, your phone would ring and if you picked it up you would hear the pre-handshaking tones.
Last year I read the book "Hack Attacks Revealed - A complete reference with custom security hacking toolkit" by John Chirillo (2001, 944 pp, ISBN 0471 41624). A large amount of hacker software was on the accompanying CDROM disk. I read the book cover to cover, not to understand most of it but to just get a feeling for what hacking can be done. My impression is that the internet is screwed. IDS and IPS efforts are pittiful compared to what the hackers can do. Firewalls (even with DMZs) are not enough.
Another book (if you are serious) I read, cover to cover, is "Malware - fighting malicious code" by Ed Skoudis (2004, 647 pp, ISBN 0131014056). Its much easier to read and understand. Last time I looked (recently) on amazon.com, you can get it used for $3.00.
I am not a computer expert.
