The Holy Quran has ordered the women to          cover themselves in some situations. 
"And say to the believing women that          they cast down their looks and guard their private parts and do not          display their ornaments except what appear thereof. And let them wear          their head coverings over their bosoms, and not display their          ornaments..." (Surah Nur          24:31) 
It is also mentioned in Surah Ahzab, "O          Prophet ! Say to your wives and daughters and the women of the believers          that they let down upon them their over garments, this will be more          proper, that they may be known and thus they will not give trouble. And          Allah is Forgiving, Merciful." 
(Surah Ahzab 49:59)         
In the same chapter, Allah says:-         
"O wives of the Prophet ! You are          not like any other of the women, if you will be on your guard, then be          not soft in (your) speech, lest he whose heart has a disease yearn and          speak a good word." 
(Surah Ahzab 49:32)         
Another verse "And when you ask them          (the wives of the Prophet) any goods, ask of them from behind a curtain,          this is purer for your hearts and (for) their hearts."(Surah          Ahzab 49:53) 
In the above verses, the Muslim woman          is ordered to veil herself. She must not come before na mehram          without Hijab. She should dress in such a manner that strange men do not          get an opportunity to glance at those parts of her body which arouse          passion; and thus make her an object of desire. It is the responsibility          of a woman to assume such poise and behaviour that she does not excite a          man's passions. Even a glance of lust can infatuate a man and a          seemingly harmless encounter eventually lead to mischief and corruption          in society, destroying entire families. 
In Iran, during the rule of the Shah          when the law of Hijab had been revoked, the cases of fornication          increased sharply. Every day tens of cases related to sexual crimes were          heard in the courts of law. Every month tens of married mothers used to          forsake their homes to enter into a perverse life of illicit sex. Five          thousand of such parents established a new township outside the city of          Tehran. 
The condition steadily deteriorated and          come to a stage that every day approximately seven infants were found          abandoned in the streets of Tehran, as reported by the commissioner. It          is obvious that illicit children born as a result of Fornication, whose          parentage is not established, cannot create a position for themselves          and are a burden to society.
Due to the absence of Hijab, adultery          and fornication became common and thousands of chaste women become          immoral. One of the highly effective ways of protecting the society from          the sin of adultery is that women wear hijab and ward off the evil          glances of sensuous men. 
