Over 500,000 fugitive illegal aliens in U.S. (catch and release)

Per this:

The U.S. Immigration and Customs Enforcement agency (ICE) says that as of Sunday, Sept. 5, it had caught-and-released 506,232 illegal aliens who are now fugtives. That is more than the population of Sacramento, California, which currently numbers 486,189.

"Fugitive illegal alien" generally means someone who was caught as an illegal alien, who promised to appear in court to answer the charge, and then who never showed up or someone who was ordered deported but never showed up. That's distinct from a "criminal illegal alien", which is an illegal alien who's committed a non-immigration crime. And, it's important to note that the figure is for all time, including the Bush administration which trumpeted having stopped "catch and release", at least on the border.

Where the Obama administration differs from the Bush administration is in this:

“It is important to note that our fugitive operations teams now can spend up to 30 percent of their time arresting convicted criminals at-large,” (Brian Hale, director of public affairs at ICE) said. “Thus, their fugitive arrests don’t reflect all of their work.”

While obviously we want to deport as many criminals as possible, the flipside is that DHS's policy is a form of de facto amnesty.