Even more would change system files and / or networking related stuff, to log your keyboard and steal passwords and phone home, or even to interfere with your online banking. Several also manipulate the system restore mechanics, to re-appear even after being removed by safety software. And worst is, they often try to get auto started extremely early after reboot, before any of your shields are up. And manipulate those then... In most cases, damaging the system to not boot anymore would not be in the interest of a bad guy, as this would also stop his misuse of your machine. This often includes spreading the malware even more over your machine, like to all of your contacts, or stealing even more critical data from you... So killing your machine kills his worthy tool. Keep in mind, after mistreating you, they may like to sell their access to other criminals, that would like to continue with hurting you and others. The first one may steal some of your internet accounts for gaming sites or e-mail, next may want to steal your bank account or attack your money transfers, third may want to spread <real dirt> or other illegal stuff over your machine. Then there are people attacking web servers they don't like. Most of all would like your system still to be up and running, at least until all they want is done... So it depends on the intention of the criminal. No more, no less.