In one word, that information is ...... "WRONG"
No offense Screwston, and if you would like to quote relevant law, I'd love to see it, but my guess would be that you can't. Wow, I just sounded like a dick, sorry man, I really meant no offense.
4th ammendment baby! teacher always helped me remember this by telling me a story of a cop with no thumb, reaching around my bag (four fingers).
Anyway, the way it works is thus: The security actually just act as if they were the local police officers, they have no more rights to search your stuff or detain you as the normal police do. Normally they have less rights, but that all depends on their classifacation. Some security officers are just joe schmoe, some are licensed PI's, others are actually police officers with renta cop badges, and others are off duty police officers, which it is really ends up helping or hurting you, so to play it safe always treat one as if they were a cop, avoids problems later on.
The cops, or security, only have the right to search your bag if (1) you consent, (2) have probable cause such as drug sniffing dogs, or (3) leave your bag open. There are other ways, but I don't feel like writing a book right now, so I'll move on. If you consent your an idiot, if they have probable cause then your fucked anyway. But if you left one of your zippers open, or slightly, that compartment is fair game, only because they could theoretically look inside that section and see something, it's open to the public, but closed bags are a no go for searches.
Also, if you had mail inside that bag, that is not open for searches, unless they have a warrant. If they searched it, then you can charge them with a number of different offenses. You can talk to a lawyer if you want, but right off the top of my head you have charges for unreasonable detention, unreasonable search, and tresspass to chattels (both your bag, and the mail). If you went to civil court, you could get the cops, and possibly their department and maybe the school, to pay you out a couple of hundred dollars. (Just estimating here, contact a lawyer if you are interested in pursuiting this)
So yeah, I'm baked, so I'm off. Hope that helped.