The first 3 are usually the most effective:
Wallpaper Hijacker Removal Tool:
http://www.majorgeeks.com/Wallpaper_Hijack_Remover_d4816.html
Note: You should hit all "Repair" buttons even though it may not say "Found!" This will fix a wallpaper hijack everytime if all repair buttons are pressed.
Malwarebytes Anti-Malware:
http://www.download.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html?hhTest=1.
Download, install, update and select Full Scan.
Remove all infections that it finds after scan.
Spybot S&D:
http://www.safer-networking.org/en/download/index.html
Download, install, update and Immunize, turn off Tea Timer then click 'Check for problems' then when complete select all and then 'Fix Checked'
Spyware Doctor Free Basic Edition - Realtime monitoring:
http://pack.google.com/intl/en/pack_installer_new.html?hl=en&gl=us&ciNum=12
Its free with Google pack, untick all boxes except Spyware Doctor. Download install, update and run.
SUPERAntiSpyware Free Edition:
http://www.download.com/SUPERAntiSpyware-Free-Edition/3000-8022_4-10523889.html
Download, install, check for updates, then select Scan your Computer, select your drive and select Perform Complete Scan
VundoFix:
http://www.symantec.com/content/en/us/global/removal_tool/threat_writeups/FixVundo.exe
Disconnect your computer from the internet
Run vundo
Restart your computer
Run the tool again to ensure no traces are left.
If there are the reboot into Safe Mode and run FixVundo again.
A-Squared Free:
http://www.download.com/A-squared-Free/3000-2239_4-10262215.html
This is not a limited version but a full tool to clean your computer from Malware, Spyware, Trojans, Backdoors, Worms, Dialers and Keyloggers.
How to use:
http://cotojo.wordpress.com/2008/07/07
If the problem persists, turn OFF System Restore and scan with the above programs in Safe Mode, Right click My computer > select Properties > System Restore Tab > Tick Turn Off System restore on all drives.
After scans are complete and machine is clean remember to turn system restore back ON and create a new restore point.