how does dsss cause interference?

How can DSSS systems like WLAN's cause interfernce with other 2.4GHz wireless devices since the information signal of a DSSS is spread via pseudo-random noise generator?

Since the inforamtion is spread over more of the spectrum than the information signal, how can WLAN's cause interference. I would think that spreading the information signal over much more of the BW would help prevent interference situations.

Please drop a line or two for an explanition please. Or a nice link that explains this "specific" concern I have.