A true genocide is taking place near Sinjar, Iraq. ISIS conquered the town of Sinjar, home to many Yezidis. Most of them fled, but some were captured by ISIS. 1,500 men were executed in front of their families. The women and children were then sold into slavery. Many of the purchasers were ISIS fighters and presumably the women are to be some sort of sex slaves or possibly wives of the fighters. The problem is that in Yezidism, the penalty for marrying or even dating outside the religion is death by stoning (warning: very graphic video at the link). These poor women are truly stuck between a rock and a hard place.
The Yezidis say they are Muslims, and I do believe that Yezidism can be seen as a highly aberrant form of Shia Islam similar to Alevism, Alawism, and Druze, if Druze can be seen as Islam at all. Yezidism also incorporates from Judaism, Christianity (especially Nestorian Orthodox Christianity) and even Zoroastrianism. At base, it appears to be a split from the original Zoroastrianism or perhaps even a precursor to that religion. Ultimately, Yezidism is a tribal religion of Iran. It may be one of the oldest religions on Earth, with forms of it dating back possibly as long as 8-10,000 YBP.
Local Arab Muslims say that the Yezidis are devil worshippers and they are widely condemned for this. ISIS calls them apostates for leaving Islam, but they were never really a part of formal Islam anyway. Yezidis however did become part of the Islamic religion around the year 1200 following a Shia Sufi prophet-type figure. Perhaps you could argue that they are heretics, but apostasy does not seem to be a correct analogy.
A good overview of the Yezidi religion is here.
Whether or not the Yezidis worship the Devil is an open question. If you ask your average Yezidi, they will insist that they do not worship the Devil. In fact, they are not even allowed to say his name. However, the religion is extremely complex, and my analysis indicated that Yezidis do indeed worship the Devil, but in their theology, the Devil is the good guy, not the bad guy. He represents good and he does only good things, and he spends all his time fighting evil. So the Devil in Yezidi theology is akin to Jesus in Christianity. The Yezidis certainly do not worship evil in any form. Instead they worship good and hate evil, like most formal religions.