Mexico City ? The Vatican on Saturday ordered the overhaul of one of the Catholic Church’s largest and most influential organizations following an investigation into decades of sexual abuse by the group’s founder and systematic efforts to cover it up.

Mexican-born Father Marcial Maciel engaged in “very serious and objectively immoral behavior,” the Vatican said — including fathering at least one child and sexually molesting boys and seminarians. The abuse dates to the 1950s and continued into the 1990s, years in which Maciel led a double life, protected by silence and obedience and his ability to sideline his accusers.

Maciel, who died in 2008 at 87, founded the ultra-conservative Legion of Christ order in Mexico in 1941. Today, the Legionaries, as they are known, operate in nearly 40 countries with 800 priests, 2,600 seminarians and a lay branch, Regnum Christi, with more than 75,000 members. In Mexico, the group controls a vast network of schools and universities that preach traditional Catholic values.

In a lengthy and sternly worded statement, the Vatican said Saturday that Pope Benedict XVI will appoint a special envoy and a commission to oversee the “purification” of the order and the “re-definition” of its secretive, militaristic culture.