Overview:
Second Thought is adware and its also a hijacker. There isn't any possible reason why you would ever want to leave this on your system. According to their terms they can contact their servers to log things like your browsing habits. They could also install additional junk on your system without your approval!

Welcome to Second Thought! We are your Internet companion to make sure you have a second opinion when you surf. We pride ourselves in broadening your knowledge of the web.
Originating Website

Their Uninstaller:

Should you wish to uninstall the program at a later date, you may request the uninstallation program by downloading it from the Uninstallation page.

Also Known As:
Adware.SecondThought
BKDR_RULEDOR.E
Second Thought
SecondThought
Trojan.Win32.SecondThought
Trojan.Win32.SecondThought.a
Trojan.Win32.SecondThought.c
Win32/SecondThought.G

Destroy Autorun:
Delete the following keys
HKEY_LOCAL_MACHINE\software\microsoft\windows\currentversion\run\adstartup
HKEY_LOCAL_MACHINE\software\microsoft\windows\currentversion\run\bokja
HKEY_LOCAL_MACHINE\software\microsoft\windows\currentversion\run\sqinstaller
HKEY_LOCAL_MACHINE\software\microsoft\windows\currentversion\run\stcloader

Reboot your system then:

Make sure you click start --> Run and type in msconfig. Then select the startup tab. Any references to the processes below.

Unregister DLLs:

Tip: this is only a list of known files/locations. You will want to do a search by the name of the file to see if they're on your system.
A while back I wrote a guide to Register/remove DLL or AX files which you will need if you don't know how to unregister these files.

Each file is in several locations so you'll need to search for them and unregister + delete them in every location you find.

2ndsrch.dll
a_clearsearch.dll
cdsm32.dll
csaolinst.dll
csbiinst.dll
csie.dll
csieinst.dll
idleui.dll
spextdll.dll
swrt01.dll
swin32.dll
voiceip.dll

End Processes (may or may not exist):
addestroyer.exe
addestroyerinner.exe
automove.exe
bokja.exe
csaolldr.exe
csv5p070.exe
loader[1].exe
slmss.exe
spedia.exe
sq_3394_3222.exesqinstaller.exe
stc.exe
stc[1].exe
stcloader.exe
trans.exe
randreco.exe

Remove Directories:
%commonprograms%\addestroyer
Program Files\addestroyer
Program Files\clearsearch
Program Files\common files\slmss
Program Files\second thought
Program Files\stc

Clean your Registry:

You should be back to normal IF this was your only problem. I suggest you post in our HJT forum since its not likely that this is your only bug. Read this first