Operation Return to Sender is the name for a massive sweep of illegal immigrants by the U.S. Immigration and Customs Enforcement (ICE) agency that began on May 26, 2006. According to ICE, the campaign has focused on individuals deemed to be the most dangerous, including convicted felons and gang members, particularly those of the notorious Mara Salvatrucha (MS-13) gang, as well as repeat offenders, some of whom had already been deported. As of late April 2007, over 23,000 illegal immigrants had been arrested.