This is a very serious questions and I hope there is a solution.  How deep can a hacker get into your personal computer?  Can they download illegal or highly classified stuff onto your computer to incriminate you?  As we all know, stuff that is simply deleted is not totally gone and can be recalled by experts at any time.  Can you PROVE that someone else hacked into your computer and did the downloading?  I have a friend who is in serious trouble and swears that what was found on his computer was not his doing.  He's sick over it and he'll most likely serve time over it.

Thanks

The answer is yes, technically someone could hack a computer and place files on it, and no there would not really be a way to tell it was done by an outsider. The reason being that as we know Windows (and most operating systems) have users. There are system users and "real" users - like when you log on. Any good hacker would mimic a real user on the machine so it looks like the files were put there by that user.

As for how hard it would be really depends on how secure your computer is. Most unwanted files put on computers are done with a numbers game. Hackers put opt spam emails and bad downloads on sites and hope the user themselves runs the download putting files on their computer. These are normally spyware (to gather info from your computer), adware (to pop up ads when you browse the web) and trojans (to allow the hacker to "use" your computer to send mass email, hack other computers, etc and not be identified... looks like you doing it). Most of these would be picked up by any Virus Software worth it weight.  A trojan could techically be used by the hacker to put other files on your computer, but again they would have only random computers that loaded the trojan to choose from, so I don't see why they would put something out there illegal to get a stanger in trouble.

But even the best security can't stop a really good hacker. As we know they can infiltrate large corp and government computers with layers and layers of security, so if someone with that skill level really wanted to put something on your personal computer with off-the-shelf security, they could.

You can also use FTP if you can figure out the computers name and password. That allows you full access to files.

But for the most part Lucky pretty much listed it all.

That is why I use 2 external Hard Drives that are only on when I need to use files off of them. One is a backup for the main. I store nothing on my computer but operating files. If you hacked me you would be going WTF this guy has nothing on his computer. No it is all on exterior HD's.

I also disconnect my connection from the internet when I am not online. Basically pull the plug so no one can access my computer.

Usually the computer keeps a record of ever thing that happens, key strokes, log in's, files uploaded and downloaded, and should show a log of someone entering thru a back door.

Thanks guys. That's pretty much what I figured. I feel so freaking bad for my friend. He's trying to gain access (from the authorities) to his hard drive so he can have another forensic expert hopefully prove he didn't do anything wrong. It's a scary situation all the way around.

Peace

Well, he's doing 180 days right now with 8 years probation after that. The hard drive is being reexamined.

I'm in charge of networks and network security for a large medical insurance company and deal with new types of hacks every day. Of course in our case it is people trying to get stuff off our computers (customers personal financial info) and not putting it on our computers. Like Lucky said, for most home computers a good hacker can get by most retail security if they really wanted to.