Well, if you want to make sure the immediate risks are totally gone, firstly go ahead, back up any important data, and reformat.
Make sure you have your Restore disk(s) or Windows CD ready for the reinstall, and if you have a restore partition on the hard drive instead, I'd suggest copying an image of it to a separate hard drive if possible, so that it doesn't get formatted with the rest of the disk.
I highly recommend that the only way to truly make sure all threats are history is to wipe the drive clean. That means if you have a restore partition for your system backup, you need to move/copy it to another hard drive if possible. If you have restore disk(s) or a Windows disk for reinstalling your system, then make sure you have them before the system redo.
Here's what I'd recommend, start to finish:
[ol]
[li]If you're using any form of broadband, and you do not have a firewalled router, then first go and buy one. Otherwise, the rest of this will practically be useless.[/li]
[li]Backup important files to separate hard drive or external media (CD, DVD, Thumb Drive, Ext Hard Drive)[/li]
[li]Verify you have your OS/Restore disk(s) handy or copy the restore partition to another hard drive.[/li]
[li]Verify you backed up EVERYTHING you want/need to keep - Favorites, Documents, Pictures, Home Videos, personal music, whatever.[/li]
[li]Download DBAN (for your choice of CD, floppy, or now, thumb drive)[/li]
[li]Load DBAN to whatever media type you chose (make sure the computer can boot from that particular media type.)[/li]
[li]Insert the DBAN media into the computer.[/li]
[li]Restart the machine - if need be, go into your BIOS settings with <Del>, <F2>, <F10>, <F11>, or whatever your computer is setup to recognize, and verify it is set to boot from that particular media type before the HDD.[/li]
[li]Once your BIOS settings are verified/changed, save and exit that, boot on into the system. You should boot to Darik's Boot and Nuke - if you got to Windows, you didn't do something correctly - go back and verify what you did.[/li]
[li]Once the DBAN screen comes up, type in
autonuke, and leave the machine running. It'll usually take at least an hour or two, so be prepared to just wait - since it CAN take many hours at times, I often just do this before going to bed.[/li]
[li]Once the DBAN wipe is complete, you'll see a black screen with something like "wipe complete, ... hit <Enter> to re-save the results file to floppy." If you see this, remove the DBAN media (assuming not already done), insert your restore/OS media, and restart the computer (If you had to backup your restore partition, now would be the time to put that back, and THEN restart the PC.[/li]
[li]Follow the appropriate steps for reinstalling your system. If you have the choice given (depends what sort of restore/OS media you have, I recommend having at least 3 partitions created - one for Windows/Program Files/Settings, 1 for Documents and such, and 1 for your Swap File or Virtual memory)[/li]
[li]Make sure your copy of Windows is up to date.[/li]
[li]Install security software. I suggest these (all are free, some you have to specify the free version):
[UL]
[LI]AVG Free Edition 8[/LI]
[LI]Windows Defender (installed by default on Vista)[/LI]
[LI]SpywareBlaster[/LI]
[LI]Online Armor Firewall[/LI]
[LI]Malwarebytes AntiMalware[/LI]
[LI]Super AntiSpyware - I'd probably just disable the auto-startup options, and only use for scanning, occasionally.[/LI]
[LI]DrWeb CureIt - not an install, but not a bad idea to keep around.[/LI]
[LI]CCleaner - not really security, but to clean out temp files, where lots of malware likes to hide.[/LI]
[/UL]You can get the first 3 of those at
and the rest at www.download.com[/li]
[li]Configure your setup to your liking - other apps, such as any sort of Office Suite, Picture/Media apps, etc.[/li]
[li]If you used imaging software to backup your restore partition... or if you have or want to buy such software, now would be a good time to create an image of your current setup in case something still happens in the future.[/li]
[/ol]
Anyway, I probably went a bit overboard in detail there. But that is what I would personally do if it were my machine, assuming I had the time, or assuming that I could do it one bit at a time over a decent stretch.
Whatever you do, don't get in a hurry, in case you might miss something.
If you have questions on any particular items in my list, ask. You can also look at the item descriptions, and read reviews of them online.
--
"If to err is human, then I must be some kind of human!" -Me