How does Yahoo check if someone is having fraud clicks? Do they check if a certain IP clicks multiple times in one day? because then couldn't someone just use a bunch of proxies and/or change their IP address to bypass that? Also is it allowed to have it so when ads are clicked, it pops up a new window? Someone suggested that to me but I thought when I read the Terms and Policies, that it wasn't allowed.
Yahoo will probably check the fingerprint of a computer (screen res, browser version, OS etc) as well as using cookies, IP, location and sessions. Modifying the code to open links in a new window is against the TOS for Google and I assume Yahoo as well.
You can read more of the policy here: No you cannot use popups. Glad you asked before doing what your friend told you to do.