I was exploring around the areas of Whiterun and I randomly get attacked by 3 Thalmors. The last one had a note on him that was basically something about them wanting my character dead. Now, I know Thalmor attacks can happen after a certain period in the main quest, but I hadn't even started the main quest, with the exception of the escape from Helgen one. I had never associated with the Thalmor on the characte, and I hadn't even seen any. What caused them to attack me, anyone know... or is it just a glitch?

They are a random encounter that is scripted to randomly appear starting at level 8.

It happens regardless if you have or have not started the MQ.

I got one after I attacked the colledge of winterhold guy before due time

wow 2 dragonpriests in one thread becareful man

it happens anytime after you reach level 8