They can be removed via the registry. The affected key is:
[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Extensions]
It is essential to check for spyware/hijackware/foistware.
Go to IE tools, internet options, general tab. Click on the cache settings
button and then 'view objects'. Delete anything you don't recognise. If you
are unsure, or no objects appear, for diagnosis purposes I REALLY like
BHODemon, available at
http://www.definitivesolutions.com/bhodemon.htm. It
does not need installing - simply unzip and run the EXE programme. It is
very easy to use.
Also, you may like to use a programme called BHOCop available here:
http://www.pcmag.com/article2/0,4149,2023,00.asp
I find this programme is a better option than IE6's ability to turn off
"Enable third-party browser extensions (requires restart)". This disables
*all* plug-ins and makes troubleshooting very difficult.
Many people like AdAware, available at
www.lavasoft.de . Make sure you keep
the signature files up to date and remember, AdAware may only remove the
current installation of spyware; it may not do anything about software that
reinstalls itself, so unless you want to get stuck in an endless loop of
hijack/cleanout/hijack/cleanout make sure you get rid of whatever is
installing the junk. See my Troubleshooting advice for information about
how to track down and get rid of spyware completely.
http://www.mvps.org/inetexplorer/Darnit.htm#tshoot
An excellent replacement for AdAware is Spybot. Again, it is a free
programme which can be downloaded from:
http://spybot.eon.net.au/