I believe that all techonology workers from other countires are legal immigrants.. All the Canadians/Irish/Indians I have worked with are legal and all pay taxes. Never heard of illegal IT immigrants...
I doubt that your information is correct..
I can only speak for mainframe shops in the midwest where I've worked at many of them. Many, many IT workers are in the "Don't ask, Don't tell mode". A few came here illegally. But most of the "illegals" are on, or overstayed a student or tourist visa and don't have permission to work.
Companies insulate themselves by contracting with a consulting firm, which in turn has a sub-contractor and a long line of plausible deniability.
But yes, in terms of sheer numbers, Mexicans win.
... and I'm not at all surprised by people disagreeing with me. People need a scape-goat.
To paraphrase Pat Buchanan "There is a mess in Washington ... and its all the fault of illegal immigrants."