Your computer is infected with malware. A quick Google for
"ad.yieldmanager.xxx" (substitution made so no one click on this) shows
that this malware is often connected with WinFixer, which gives you at
least one Vundo trojan variant.
Do the preparatory steps here:
http://www.elephantboycomputers.com/page2.html#Removing_Malware
Then do the specific removal steps here:
http://www.elephantboycomputers.com/page2.html#Winfixer - Winfixer
You can also check to see if there are targeted removal steps for your
malware here:
Bleeping Computer removal how-to's -
http://www.bleepingcomputer.com/forums/forum55.html
When all else fails, run HijackThis and post your log in one of the
specialty forums listed at the first link above (not here, please).
Not all tools used will work in Vista and you will need to run them
elevated. Since Vista is so new, it will be a while before removal
techniques and tools are developed. If you are unable to remove the
infection by following the general steps, register at one of the
HijackThis forums as suggested.
Standard caveat: If the procedures look too complex - and there is no
shame in admitting this isn't your cup of tea - take the machine to a
professional computer repair shop (not your local version of
BigComputerStore/GeekSquad). Please be aware that not all local shops are
skilled at removing malware and even if they are, your computer may be so
infested that Windows will need to be clean-installed. Have all your data
backed up before you take the machine into a shop.
Malke
--
Elephant Boy Computers
www.elephantboycomputers.com
"Don't Panic!"
MS-MVP Windows - Shell/User