Sounds like a Common Orb Weaver. (Or a Jeweled Orb Weaver, but I'd bet on the first one.) Google Image search for that name and you'l be bound to see the guy you're talking about.
I see these guys everywhere around dwelling...in windows, outside back doors, under porch lights, etc...and they're out in full force right now.
They are primarily brown and yellow -- and, yes, they do have a black/yellow/red/white (depending on it's color variation) square-shaped marking on the underside of their abdomen.
These guys CAN bite, but only if very provoked, and they're not poisonous, so don't worry. BTW...if you catch one spinning it's web, check it out. Orb weavers spin the "traditional" circular webs, and it can be fascinating to see them in action.
Wildlife biology student / Non-profit public garden intern...
and a good insect/arachnid ID book ;)
· 1 decade ago