The people that actually can and do hack, will not outright tell you they are going to do it. You will make them mad and then the next day your PC will be wiped or all your passwords changed and such. Good hackers (i.e. the ones to worry about) will do serious damage. Bad hackers (i.e. most of em) might be able to stop your internet for a while or get into one or two accounts but if they are dumb enough to tell you they are doing it, you can charge them with internet crimes which carry some serious sentences.
My e-mail was among a bunch of the hotmail account passwords that got leaked. My WoW account got hacked 2 days later. It took a couple of hours but I changed every password and recovered every account attached to that e-mail. Those are the hackers to worry about. I never saw him coming and he probably never met or knew me.
I was lucky enough to be on a Vent server with my GF and friend and they saw me log in.
GF: "Thought you stopped playing WoW?"
Me: "I did. It's innactive."
GF: "Demort just logged in."
I immediately connected the dots after reading the article here about the hacked e-mail addresses.
Me: "I gotta go!"
Disconnected from vent and flew through WoW, my bank website, my credit card websites, social networking sites and changed all the passwords. The dude used my hotmail address to get access to my yahoo address. That was the hardest one to recover but I got it all done within about an hour. He didn't do anything to my WoW account and I don't think he had time to attack my bank or credit cards. Weird... how the first thing someone went after was my WoW account.
Since then, my girlfriend and her brother's accounts got hacked. I am guessing through some sort of spyware. Then my friends got hacked, don't know how they did that.
Anyway, if you piss of a serious hacker, they can knock out your firewalls and fuck your shit up and do it just for the lols but you won't know who it is or why. After they were done they would go about doing whatever real crimes they were actually up to. Those darn Blackhats.