If your life or life of a member of your family is under threat just because of your faith, you are allowed to hide your faith, or you are allowed to say as opposed to whay you actually believe.
This is called 'takiyye' in Islam.

One of the companions of Hz Mohammed, Ammar and his parents were tortured by non-believers as he became a Muslim. He was forced to denial of his belief by torturing his father and mother heavily. His father and mother died of severe torture. As he was exposed to excruciating torture he said what he was asked for by non-believers. However, it was just a denial in words, but not one from the heart. Hz Mohammed told him if he was exposed to such a torture again he would say in the same way.

If your properties or money are under threat you are allowed to tell lies.
This is also called 'takiyye'

Nobody tells the truth when they are threatened by robbers. It wouldn't be wise just for sake of telling the truth.

Takiyye doesn't mean you are allowed to tell lies about issues related to Islam in order to spread your belief.

Every thing is distinctly stated in the Koran. Nobody is allowed, or licensed to state otherwise.

Takiyye isn't one of the principles or prays in Islam, but just a permission to tell such lies to save your life, properties, money, etc. in such cases.

kadersokak,
its not that innocent with cheating as you describe above. it is allowed at any time under any circumstnces.
and one of the names of allah is a great deceiver. just wonderful!
while other two religions dont allow such behaviour.

i guess islam is the only religion that obsessively defends itself even using lies.

In Islam women don't perform their daily prayers when they are on menstruation period because a woman who is menstruating can't keep ablution as blood keeps flowing from her body on her period. Ablution is a prerequisite for a prayer. And they aren't obliged to make up those prayers they missed during their periods.

That's not because menstruation is considered dirty or blood is impure. Ablution is not only getting clean physically but also getting ready spiritually for a prayer.
And there are some principles to keep an ablution. One of them is; you mustn't bleed in any way.