What follows below is the CDF clarification:
"Following the publication of the interview-book Light of the World by Benedict XVI, a number of erroneous interpretations have emerged which have caused confusion concerning the position of the Catholic Church regarding certain questions of sexual morality. The thought of the Pope has been repeatedly manipulated for ends and interests which are entirely foreign to the meaning of his words – a meaning which is evident to anyone who reads the entire chapters in which human sexuality is treated. The intention of the Holy Father is clear: to rediscover the beauty of the divine gift of human sexuality and, in this way, to avoid the cheapening of sexuality which is common today.
"Some interpretations have presented the words of the Pope as a contradiction of the traditional moral teaching of the Church. This hypothesis has been welcomed by some as a positive change and lamented by others as a cause of concern – as if his statements represented a break with the doctrine concerning contraception and with the Church’s stance in the fight against AIDS. In reality, the words of the Pope – which specifically concern a gravely disordered type of human behaviour, namely prostitution (cf. Light of the World, pp. 117-119) – do not signify a change in Catholic moral teaching or in the pastoral practice of the Church.
"As is clear from an attentive reading of the pages in question, the Holy Father was talking neither about conjugal morality nor about the moral norm concerning contraception. This norm belongs to the tradition of the Church and was summarized succinctly by Pope Paul VI in paragraph 14 of his Encyclical Letter Humanae vitae, when he wrote that 'also to be excluded is any action which either before, at the moment of, or after sexual intercourse, is specifically intended to prevent procreation—whether as an end or as a means.' The idea that anyone could deduce from the words of Benedict XVI that it is somehow legitimate, in certain situations, to use condoms to avoid an unwanted pregnancy is completely arbitrary and is in no way justified either by his words or in his thought. On this issue the Pope proposes instead – and also calls the pastors of the Church to propose more often and more effectively (cf. Light of the World, p. 147) – humanly and ethically acceptable ways of behaving which respect the inseparable connection between the unitive and procreative meaning of every conjugal act, through the possible use of natural family planning in view of responsible procreation.
"On the pages in question, the Holy Father refers to the completely different case of prostitution, a type of behaviour which Christian morality has always considered gravely immoral (cf. Vatican II, Pastoral Constitution Gaudium et spes, n. 27; Catechism of the Catholic Church, n. 2355). The response of the entire Christian tradition – and indeed not only of the Christian tradition – to the practice of prostitution can be summed up in the words of St. Paul: 'Flee from fornication' (1 Cor 6:18). The practice of prostitution should be shunned, and it is the duty of the agencies of the Church, of civil society and of the State to do all they can to liberate those involved from this practice.
"In this regard, it must be noted that the situation created by the spread of AIDS in many areas of the world has made the problem of prostitution even more serious. Those who know themselves to be infected with HIV and who therefore run the risk of infecting others, apart from committing a sin against the sixth commandment are also committing a sin against the fifth commandment – because they are consciously putting the lives of others at risk through behaviour which has repercussions on public health. In this situation, the Holy Father clearly affirms that the provision of condoms does not constitute 'the real or moral solution' to the problem of AIDS and also that 'the sheer fixation on the condom implies a banalization of sexuality' in that it refuses to address the mistaken human behaviour which is the root cause of the spread of the virus. In this context, however, it cannot be denied that anyone who uses a condom in order to diminish the risk posed to another person is intending to reduce the evil connected with his or her immoral activity. In this sense the Holy Father points out that the use of a condom 'with the intention of reducing the risk of infection, can be a first step in a movement towards a different way, a more human way, of living sexuality.' This affirmation is clearly compatible with the Holy Father’s previous statement that this is 'not really the way to deal with the evil of HIV infection.'
"Some commentators have interpreted the words of Benedict XVI according to the so-called theory of the 'lesser evil'. This theory is, however, susceptible to proportionalistic misinterpretation (cf. John Paul II, Encyclical Letter Veritatis splendor, n. 75-77). An action which is objectively evil, even if a lesser evil, can never be licitly willed. The Holy Father did not say – as some people have claimed – that prostitution with the use of a condom can be chosen as a lesser evil. The Church teaches that prostitution is immoral and should be shunned. However, those involved in prostitution who are HIV positive and who seek to diminish the risk of contagion by the use of a condom may be taking the first step in respecting the life of another – even if the evil of prostitution remains in all its gravity. This understanding is in full conformity with the moral theological tradition of the Church.
"In conclusion, in the battle against AIDS, the Catholic faithful and the agencies of the Catholic Church should be close to those affected, should care for the sick and should encourage all people to live abstinence before and fidelity within marriage. In this regard it is also important to condemn any behaviour which cheapens sexuality because, as the Pope says, such behaviour is the reason why so many people no longer see in sexuality an expression of their love: 'This is why the fight against the banalization of sexuality is also part of the struggle to ensure that sexuality is treated as a positive value and to enable it to have a positive effect on the whole of man’s being' (Light of the World, p. 119)."
See also a post from September- censoring the scope of the desire.