The "Illuminati" is just another name for Satanism. It is the same thing as Freemasonry. Basically, they are a group of "well-bred" individuals from every class of society who have rejected the Truth as taught by Christ and as handed down by Christ's Mystical Body (the Catholic Church). God spoke about the Illuminati back in the Old Testament, where we find Him say in the Book of Wisdom:
"For they say to themselves, with their misguided reasoning:
'Our life is short and dreary,
nor is there any relief when man's end comes,
nor is anyone known who can give release from Hades.
By chance we came to birth,
and after this life we shall be as if we had never been.
The breath in our nostrils is a puff of smoke,
reason a spark from the beating of our hearts;
put this out and our body turns to ashes,
and the spirit melts away like idle air.
In time, our name will be forgotten,
nobody will remember what we have done;
our life will pass away like wisps of cloud,
dissolve like the mist
that the sun's rays drive away
and the heat of it overwhelms.
Yes, our days are the passing of a shadow,
from our death there is no turning back,
the seal is set: no one returns.
Come then, let us enjoy what good things there are,
use this creation with the zest of youth:
take our fill of the dearest wines and perfumes,
let not one flower of springtime pass us by,
before they wither crown ourselves with roses.
Let none of us forgo his part in our orgy,
let us leave the signs of our revelry everywhere,
this is our portion, this the lot assigned us.
As for the virtuous man who is poor, let us oppress him;
let us not spare the widow,
nor respect old age, white-haired with many years.
Let our strength be the yardstick of virtue,
since weakness argues its own futility.
Let us lie in wait for the virtuous man, since he annoys us
and opposes our way of life,
reproaches us for our breaches of the law
and accuses us of playing false to our upbringing.
He claims to have knowledge of God,
and calls himself a son of the Lord.
Before us he stands, a reproof to our way of thinking,
the very sight of him weighs our spirits down;
his way of life is not like other men's,
the paths he treads are unfamiliar.
In his opinion we are counterfeit;
he holds aloof from our doings as though from filth;
he proclaims the final end of the virtuous as happy
and boasts of having God for his father.
Let us see if what he says is true,
let us observe what kind of end he himself will have.
If the virtuous man is God's son, God will take his part
and rescue him from the clutches of his enemies.
Let us test him with cruelty and with torture,
and thus explore this gentleness of his
and put his endurance to the proof.
Let us condemn him to a shameful death
since he will be looked after - we have his word for it.'
This is the way they reason, but they are misled,
their malice makes them blind.
They do not know the hidden things of God,
they have no hope that holiness will be rewarded,
they can see no reward for blameless souls.
Yet God did make man imperishable,
he made him in the image of his own nature;
it was the devil's envy that brought death into the world,
as those who are his partners will discover. (Wisdom 2:1-24)"