40% of so called illegal aliens are documented aliens here on expired visas.
Once your visa expires, you are unlawful presents in the country, You are illegal.
"What if I Decide to Stay Longer and am Out-of-Status with the Department of Homeland Security?
You should carefully consider the dates of your authorized stay and make sure you are following the procedures. Failure to do so will cause you to be out-of-status.
Staying beyond the period of time authorized, by the Department of Homeland Security, and out-of-status in the U.S., is a violation of U.S. immigration laws, and may cause you to be ineligible for a visa in the future for return travel to the U.S. If you overstay the end date of your authorized stay, as provided by the CBP officer at a port-of-entry, or United States Citizenship and Immigration Services (USCIS), your visa will generally be automatically be voided or cancelled, as explained above." http://travel.state.gov/visa/temp/info/info_1...
". Consequences of Overstaying a Visa:
Some of the consequences of overstaying a visa are:
Overstays may be barred from returning to the US for ten years or three years depending on the period of overstay
Overstays may be further restricted from Extension of Stay or Change of Status
Overstaying will void your existing visa
Overstays generally are unable to obtain a new visa except in their country of nationality
Overstays may not be able to Adjust Status in the U.S.
These consequences may be considered as below:
(i) Inadmissibility as a consequence of Overstaying a Visa
The 1996 reform created two new grounds of inadmissibility for foreign nationals who remained in the US after the expiration of the period of stay authorized by the Attorney General through the immigration inspector at the time of entry.
The Three Year Bar: Persons who remain in the US after their authorized stay has expired for more than 180 days but less than one year, and who leave the US prior to the institution of removal proceedings, are barred from reentering the US for three years from their date of departure.
The Ten Year Bar: Persons who remain in the US after their authorized stay has expired for more than one year, and who leave the US prior to the institution of removal proceedings, are barred from reentering the US for ten years from their date of departure.
(ii) Bar to Change of Status and Extension of Stay as a consequence of Overstaying a Visa
Persons who remain in the US after their authorized period of stay are not able to extend their stay in the US or change their status to another nonimmigrant status. In most cases they are also barred from adjusting their status from that of a nonimmigrant to that of an immigrant." http://www.visapro.com/Immigration-Articles/...