Just fixed my brother’s family’s computers and found the direct answer rather elusive even when hunting online, so in case anyone else encounters a similar problem here are the details:
a. Google search results were coming up ok, but when clicked on intermittently redirected to K-Directory or Search.Pro pages
b. Various dodgy pop-ups and other redirects were occasionally happening
c. Problem was happening on more than one computer
d. The largest collection of anti-virus and anti-spyware programs collected on a machine this side of Offa’s Dyke picked up a few small issues but didn’t fix matters
The answer? A worm had got at the router, resetting the DNS settings from automatically taking the ISP’s DNS settings to specifying two DNS servers that most of the time worked normally but every now and then slipped in a dodgy redirect.
The solution? Login to the router, change the settings on the router back to automatically accept ISP’s DNS settings and improve the router’s security (password and firmware version).
The dodgy DNS servers which were causing the problem were 188.8.131.52 and 184.108.40.206.