Lies and Deception of Muslims: it's taught in their books

Muslims are allowed to lie to unbelievers in order to defeat them. There are several forms:

• Taqiyya (Shia) or Muda'rat (Sunni): 
tactical deceit for the purposes of spreading Islam.

• Kitman: deceit by omission.

• Tawriya: deceit by ambiguity.

• Taysir: deceit through facilitation 
(not having to observe all the tenets of Sharia).

• Darura: deceit through necessity 
(to engage in something "Haram" or forbidden).

• Muruna: the temporary suspension of Sharia in order that Muslim immigrants appear "moderate".

Though not called taqiyya by name, Muhammad clearly used deception when he signed a 10-year treaty with the Meccans (known as Hudaibiya) that allowed him access to their city while he secretly prepared his own forces for a takeover. The unsuspecting residents were conquered in easy fashion after he broke the treaty two years later. Some of the people in the city who had trusted him at his word were executed. 

Another example of lying is when Muhammad used deception to trick his personal enemies into letting down their guard and exposing themselves to slaughter by pretending to seek peace. This happened in the case of Ka'b bin al-Ashraf (as previously noted) and again later against Usayr ibn Zarim, a surviving leader of the Banu Nadir tribe, which had been evicted from their home in Medina by the Muslims...

Such was the reputation of early Muslims for lying and then killing that even those who "accepted Islam" did not feel entirely safe. Consider the fate of the Jadhima. When Muslim "missionaries" approached their tribe, one of the members insisted that they would be slaughtered even though they had already "converted" to Islam to avoid just such a demise. However, the others believed they could trust the Muslim leader's promise that they would not be harmed if they simply offered no resistance. (After convincing the skeptic to lay down his arms, the unarmed men of the tribe were quickly tied up and beheaded - Ibn Ishaq 834 & 837)...

Leaders in the Arab world sometimes say one thing to English-speaking audiences and then something entirely different to their own people in Arabic. ..

~End quote. Go here for the full article with a dozen examples from the quran,hadith, and Islamic law, as well as historical examples.