Do a malware check with several malware scanning programs on the Windows computer. Please scan with all programs because each program detects different malware. All these programs have free versions.

Make sure that you update each program to get the latest version of their databases before doing a scan.

• Malwarebytes' Anti-Malware:
  http://www.malwarebytes.org/mbam.php
• AdwCleaner:
  http://www.bleepingcomputer.com/download/adwcleaner/
  http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked
• https://support.mozilla.org/kb/troubleshoot-firefox-issues-caused-malware

Tell me if this solved your problem ,or you need more help.

At the bottom of that Yahoo page, is there a tiny "Learn More" link below the search box which leads to a page describing the MyBrowserBar Network Error Assistant which you can disable from the Spigot toolbar?

I suggest getting Spigot off the computer completely. Likely it can be found on the Add-ons page. Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

If there's no Remove button there, use the Windows Control Panel, Uninstall a Program, to remove it. In that dialog, I suggest clicking the "Installed on" column heading so you can see whether any other bundle items snuck onto your system recently.

Was that it?