It's a very popular misconception that when people abbreviate Christmas as "Xmas" they're going along an attack plan to get 'Christ out of Christmas.'
In reality, the usage of Xmas can be traced all the way back to 1021. X stands for the Greek letter Chi, which is the first letter of the word Christ in Greek.
When monks in Great Britain translated ancient texts into Old English as far back as the year 1021, they would write X instead of Christ. The first recorded usage of Xmas dates all the way back to 1551.