Well, not today, but on this day 92 years ago. What brilliant plan did the lone thief come up with? He simply walked in and carried it out under his clothes.
I've (barely) seen the Mona Lisa myself, and I can assure you that it's much more securely guarded now. As secure as anything in France can be, anyway.
Here's a good French joke:
Why did the French plant trees along the streets of Paris?
So the Germans can march in the shade.