lol u people are so funny, what is so important can be on your computer that u'd be afraid of hackers? cuz if i real hacker wants to get into your computer firewalls and other **** wont stop him. and lame wanabies wont be able to do anything unless u setup some trojan server on your own.
and to answer your question, if u just booted up and didnt log in yet , your computer is not connected to internet so noone can see you online. if u just hit "win+L" then everything is still loaded and you are connected to internet and all. but when u go to start>log off> log off . then everything supposed to unload.