Undocumented Mexican youths who came to the United States as children reacted with joy to an Obama administration rule change on Friday that could spare them deportation, although opponents slammed it as amnesty and ridiculous.

"It hasn't really sunk in entirely, but I feel a sense of joy and happiness because I know this is really going to change my life," said Justino Mora, 22, an undocumented computer science student at UCLA in Los Angeles.

Mora is among an estimated 800,000 illegal immigrants up to 30 years old who came to the United States as children and will benefit by the surprise order announced by U.S. Homeland Security Secretary Janet Napolitano.

"I will have the opportunity to ... create my own business so that I can help ... my family financially and create the jobs that the U.S. needs," Mora told Reuters.

The rule change applies to undocumented youngsters like Mora who do not pose a risk to national security and who will now be eligible to stay in the country and apply for work permits. Mora came to the United States at age 11 from central Mexico with his mother.

Those eligible under Obama's plan must have come to the United States under the age of 16 and lived in the country for at least five years. They must be in school or have graduated from high school or be honorably discharged from the U.S. military. They also must not have been convicted of any felony or significant misdemeanor offenses.

For 18-year-old high school honors graduate Yolanda Medina, in Phoenix, Arizona, the rule change means a shot at studying at the city's Grand Canyon University in the fall and the chance to escape a life toiling in menial jobs open to illegal immigrants.

"Most of us ... are forced to take jobs like cleaning houses, cleaning someone's car or babysitting, when you have so much more to offer," said Medina, who came to the United States with her mother from Durango, Mexico, at age 3.