What would you do if you were accused of doing something you didn't do?

Ok so I am pretty new on my job. I have been there for almost 9 months. I have tried to maintain my work ethic and integrity. I have stayed out of drama, tried not to talk about others and just kept my cool when things were overwhelming. Let's face it, jobs right now are a hard commodity to find and although I haven't gotten a raise I still need my job. It pays the bills. So imagine my surprise when I was pulled into the office and accused of downloading a game on my shift. First of all, in my defense, I am NOT the type of person to DOWNLOAD anything ESPECIALLY AT WORK!! NEVER EVER! That's just not something I would ever do. I look at it like this. Those aren't my computers and I wouldn't want someone to come to my house and download things on mine. I am very aware of spyware and adware which can be potentially harmful to computers. We rely on our PCs at work. In fact when they are broke down it's that much more difficult to do the job correctly. So, anyway my boss informs me that while I downloaded this game, it had spyware and caused a virus on the computer which then had to be re-phased. You have to understand I am the only one who works on third shift. So it's my word against hers. She had this piece of paper in her hand which had many different syllables and numeric symbols. It was greek to me. It never stated the name of the game in which I was supposed to download. She said she did some research and it was when I was on duty. FIGURES! But here is the very interesting part. It was at 6:39AM about the time the first shift person came in at 7. Now I don't know about you, but if you were going to download a game and then delete it before anyone found out, wouldn't you do it long before it was almost time to go home? I mean common sense tells you that, right? IF I did download something which had a virus in it, IT WASN'T intentional in the least! In fact, there are times when we have to look up things which pertain to our job. I can't lie and say I have never looked up other things. But you can't play games online. I feel like I have been singled out for doing something I have seen others doing. But they didn't get into trouble. I DID! I swear I am the ONLY person I know who tries the hardest to behave and gets into trouble. It seems to follow me. So now, the worst part is my boss thinks I sit on my bum all night and plays games. I sure wish that was the case. Anyone I work with can attest to the fact that I work HARD. I don't sit at the computer and I certainly do not play games!!! It frustrates me because I have no way to defend myself. -Question- If someone else had downloaded something earlier in the night, and I had shut the computer down and restarted it, could it have looked as if I was the one who had downloaded the game and the virus? Any techies out there? Please help me! I am so confused I just want to quit my job and say **** it!