hi my mac is slow and i think i have a virus on it this page kips coming up every time i open any internet window

You do not have a virus. You might have an adware/malware on your browser.

Start by relaunching Safari with the Shift key down. If that doesn't help restart your Mac in Safe Boot mode.

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Restart in Safe Boot mode by holding down the Shift key at startup. Safe Boot is quite slow because the OS performs some cleanup and verification tasks, so give it time. After you're completely logged in, restart normally.

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Reading this might also be helpful.

Mac Malware Guide: How do I protect myself? http://www.thesafemac.com/mmg-defense/