Note that many websites have their own advertising, unrelated to adware.
Cytron is an Internet Explorer Browser Helper Object. It scans the content of pages being viewed for keywords and opens pop-up advertising when they are detected
First deregister the Cytron BHO. Open a DOS command prompt (Start->Programs->Accessories) and enter the following commands:
regsvr32 /u "%WinDir%\Downloaded Program Files\potd.dll"
(Change potd.dll to sec.dll if you have Cytron/sec variant.)
You should then be able to delete the 'TargetingSource' entry in Downloaded Program Files (in the Windows folder), and the registry key HKEY_CURRENT_USER\Software\POTD (Start->Run->regedit).