here:
"How can undocumented entry and immigration status violations lead to inadmissibility?

Anyone who comes to the US without permission of the USCIS or State Department is inadmissible. Failure to attend removal proceedings without a good reason makes a person inadmissible for five years. Anyone who engages in fraud or misrepresentation in an effort to enter the US is inadmissible, as are those who have made a false claim of US citizenship. Those who violate the terms of a student visa are also inadmissible for five years."

from this website:http://www.visalaw.com/05apr1/2apr105.html