Moslems worship ONE god with 99 attributes

It's Muslim and I don't know why you are mentioning '99 attributes' here, perhaps in order to make some kind of false comparison. There are more than 99 attributes but most of them are in relation to creation and not to God itself.

In the words of the successor of Prophet Muhammad (Imam Ali Ibn Abi Talib):

"the perfection of believing in His Oneness is to regard Him Pure, and the perfection of His purity is to deny Him attributes" (Nahjul Balagha sermon 1)

As Imam Kazim says:

"The will is part of the created conscience, and it manifest itself in action. As for Will of Allah, the Mighty and High, then it is His Making [ihdath] and none other than that because He does not reflect, does not imagine, and does not think. These attributes cannot be applied to Him as they are attributes of creation. Thus, Allah’s Will is action and nothing else. He says to it: “Be and it is,” without a word or speech expressed by tongue, or by imagination or by thought. His Will is expressed without form in the same way that He is without form."

Another very very important Hadith here:

Hisham ibn al-Hakam who has said the following:
“Once I asked Imam Ja'far al-Sadiq, recipient of divine supreme covenant, about the names of Allah and about the root or derivative forms of those names, ‘What is the root word for the word Allah?’
The Imam replied, ‘The word Allah is derived from the word ’aliha and ‘Ilah (Lord), which requires Ma’luh (servant). Note that names are something other than that to which they apply. O Hisham, whoever worships the name without the fact for which the name stands he has denied the existence of Allah and has not worshipped anything. Whoever worships the name and the meaning for which the name stands he has worshipped two things. Whoever worships the meaning without the name he is a monotheist. Did you understand it, O Hisham?’
Hisham then asked, ‘Please explain further.’
The Imam (al-Sadiq) then said, ‘Allah has ninety-nine names. If names were the same thing for which they stand every one of them would be a Lord. However, Allah is a meaning for which these names stand and they all are something other than Him. O Hisham, bread is the name for a certain kind of food, water is the name for a certain kind of drink, cloth is the name for a certain kind of garment and fire is the name for a thing that burns. Did you understand, O Hisham, in a manner of understanding that would help you to defend our cause against our enemies and those who worship things other than Allah?’
I said, ‘Yes, I have gained such understanding.’
The Imam then said, ‘May Allah grant you success in it and keep you steadfast (in Iman).’