Yeah it also could be a torrent, because if you delete the torrent file in e.g. utorrent, then the map with the file will still exist (although it should be empty.) when you delete it you will get your gb back.
well it was like this i download malware antimalware with key so i SCAN with avast the rar file and a blue screen appears i restart and then i got 1gb less i didn't open the key file or extract it no i just scan it and that happend
It didn't cost you anything. You GAINED 1GB of free space if you went from 136 to 135.
What you really need to be asking is - does all your shit still work, are you missing stuff you normally use, or have stored for backup in the past.
If you're really THAT concerned about it... Backup your important shit to a CD/DVD/USB drive, whatever.. make sure its clean. Then just reformat your machine and put windows back on, or have a nerd you cheat off in class do it for you.