How do you block a web site from pop up?

Some unneeded software advertisements for anti-spyware got on my computer at the bottom at the right hand corner and I can not remove it. It is always comming up with a message about spy war and viruses that I have. When check with Yahoo Anti-spyware, I removed what was dangerous and also Yahoo Anti-Spyware had the two advertise sites as medium threat. I eliminated them yesterday. I now also have tabs/buttons below my Yahoo Web Search at the top that are all for this unneedd and not wanted antispyware. How do I remove those buttons

How do you block a web site from pop up?antivirus programs

(1) Get you self a good antivirus or a free one if your present anti virus is not protecting you .

(2) If you have not already scanned your comp with spybot do that now .Update it and then run it so it gets rid of all the spyware and trojans in safe mode

(3a) Do an online virus scan to check if you still have any other viruses in your computer. And let us know if the online virus scan still finds any virus or spyware .

How do you block a web site from pop up?computer protection

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just allowed the pop ups