Guys, on thief page i see:

Windows installer 2.0.0
and
Universal Update 2.0.3

What is it?

Use both, first the installer then the update.

The Universal Update is a patch, provided as a separate download for those who already had the game and didn't want to re-download the large installer just to get the patch. If you are downloading the game for the first time, download both and run the installer and then the update, as xtharpe said.

well... i think we are not in stone age and 600mb is not a big deal, i prefer to have updated installer, rather then installing game + patch + patch + patch like in good old times....)

p.s. but that's me...

They could update installer and post patch for those who downloaded old version.