Do a malware check with some malware scanning programs on the Windows computer.
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.

• http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware
• http://www.superantispyware.com/ - SuperAntispyware
• http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page
• http://www.safer-networking.org/en/index.html - Spybot Search & Destroy
• http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

I believe you have probably identified correctly where you picked up the problem, places such as Google advertising, coupon sites and the like. It is IntelliTXT or similar that you are describing. Word with double green or double blue underlining.

I have to protect my own pages from that, but you are visiting pages where ad revenues are their only concern, or main concern.

• When visiting sites (including Firefox's help page!) I am seeing double underlined links in green type randomly throughout website pages that link to a Groupon subscriber site. Is my machine compromised, or is it just Firefox 5.0? | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/questions/846179
• did you guys put text enhance in the firefox browser? | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/questions/871383

By the way, I do not see IntelliTXT ads on the page, largely because of "Adblock Plus" extension, see the replies in question listed above which say to include "EasyList" filters after installing the extension. Shown here in display are the files blocked and the filters blocking them in this case the one pointed was blocked by both EasyList (USA) and by Fanboys.

What I don't understand is, why am I only seeing these links when using FF? They don't display on IE or Chrome.

Did you do the malware check?

You may have caught malware that (currently) only targets Firefox.

Create a new profile as a test to check if your current profile is causing the problems.

See "Basic Troubleshooting: Make a new profile":

• https://support.mozilla.com/kb/Basic+Troubleshooting#w_8-make-a-new-profile

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" in case there are still problems.

If that new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files.

See:

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

My technical expertise is somewhat limited to be honest. (not sure what you mean about creating a new profile for instance - bit beyond my capabilities I'm afraid). Am working through the list of malware scanning programmes you suggest; just the lavasoft to go now. There were threats to be deleted & have allowed that. Will reinstall FF again (unistalled now) when finished & see what happens.

From what you have described, I don't think you are ever going to pick that up as malware at all. But I did look at the site you mentioned in Google Chrome, and in IE9. First thought was maybe Chrome suppresses it, but that would be contrary to trying to convince you that their AdSense or IntelliTXT is "helping" you.

What I did find in Chrome was "Google Chrome's connection attempt to ad-apac.doubleclick.net was rejected. The website may be down, or your network may not be properly configured."

Since I don't have ad blockers in Chrome or IE, that tells me that my hosts file is doing its job, you can draw you own conclusions. There is something similar displayed in IE, but I can't read what was there because the font-size was too big. for the space. In Firefox with "Adblock Plus" extension it is all wiped out. The hosts file works across the entire system but is directed at blocking malware sites more than advertising. "Adblock Plus" is very good at blocking ads and can do its blocking with more generic filters, and can block a lot of malware from coming in but it can't block at the system level that a hosts file can.

In IE although I can only see "It appea" because the font is too large and text does not wrap it does actually say "It appears you are connected to the Internet, but you might want to try to reconnect to the Internet."

I would certainly suggest installing "Adblock Plus" extension and the "Easylist (USA)" filter subscription -- links are in the links previously provided, and installing the hosts file as well also in the links.

It takes a bit more work to install and maintain a hosts file but the directions should be clear enough.

thanks dmc & others for your help. As explained though my technical expertise is not the greatest. I've restored my computer which has fixed a lot of probs; however am a bit nervous now to download FF again. I installed it initially because was having problems with lines across the website I'm building with one of the build it yourself sites (only happened on IE). Firefox gave the best view even over Chrome. So...because as I explained my expertise is limited, it takes me hours (which I don't really have) to try and work out the suggestions/solutions offered. Can anyone just tell me what I should do/install or otherwise, before I re-download FF to avoid any more nasties?

PS....when I run spybot, this appears (attached) re: Zango. When try to fix tells me can't fix & need to try again as Administrator - which I am. Tried twice now & won't fix. ?????aaah