I wonder if anyone can help with this - it started a couple of days ago but is getting worse.  All our bookmarked pages seem fine but if we try to search for something we are not getting what we are searching for (to put it mildly).  We use Google and, for example, I just put in 'London Travelcard' and was, as top choice, given London Travelcard FAQ which looked fine.  On choosing this I was taken to what is obviously a hardcore porn site which has on its front page (amongst options which I can't list here) sponsored sites - for example London Travelcard FAQ or Travelling to London.  I don't go into these in case they are not what they say and just go straight 'back' but this is happening with almost everything we search for.  Some other options Google gives are OK but it is not just the top option, I have tried others and got similar sites.  Does anyone know how to stop this or what may be causing it.  We are not exactly computer experts and don't have a clue where to start and we are beginning to get really worried about this.
Many thanks
Alex

Sounds like you may have something dodgy on the PC.  First thing I would do is to delete the history and cookies from IE (I assume you are using MS Internet Explorer?).  Do you have anti virus software? If so run a full scan.  Download anti popup software, I use Adaware which you can get from www.lavasoft.com (the personal edition is free) run it and delete any stuff it finds.

To prevent it happening again make sure you have a firewall setup.

Thank you.  Will wait for partner to get in and do all you suggest.  We have Norton antivirus and a firewall set up so I am not sure how this happened unless we've managed to disable something, which is perfectly possible.  Will let you know what happens and many thanks.

In addition to the above yo could also install Spybot.  It catches what Ad-Aware doesnt ;)  I have both and between them they've made my computer easier to run :)

You can also block specific sites through Internet Explorer options.  Use the facility that allows you to type in specific sites to allow or disallow, so the particularly nasty ones are blocked every time :)