In the Catholic Church there are no such things as sects or secret societies. Opus Dei is a personal prelature of the Catholic Church, a well known juridical configuration in Canon Law.
Further, I will mention the recent celebration of the 70th anniversary of the foundation of Opus Dei (2 October 1998). The faithful of the Prelature and others assembled together with Cardinal Hume in a Thanksgiving Mass, in which the Cardinal expressed how Blessed Josemaria Escriva, founder of Opus Dei, "understood that he was to urge men and women in all walks of life to seek holiness and carry out an apostolate in the midst of the world, through the exercise of their profession or trade, without a change of life ... but surely always a constant change of heart! But already these words, seventy years ago, anticipated the Vatican Council's decree on the place and the role of the laity in the world".