This here. The most important thing on your computer are all your session cookies, which are, well, accessible with permissions your user account already has.

Dudes don't care about making your shit into a botnet, or putting a rootkit in your firmware, or whatever other technically complex thing you care to think about: they're there to steal your shit, and the most valuable shit you have is sitting there out in the open for the taking for anyone who makes it past a very very low bar of 'make the user do something stupid'.