Suppose $S$ is a set of known websites which are very important. Assume there is an anti-phishing tool company $A$ which is aware of such websites. Can the company A reliably develop an anti-phishing tool just to distinguish the websites of set $S$ from its complement $S'$? In other words is it possible for the anti-phishing tool to notify its users if the currently visited website is from set $S$ or set $S'$?
I think this problem is relatively easy as the anti-phishing tool has to distinguish between set $S$ of known websites from the complement set $S'$. Or can such anti-phishing tool can be fooled?
Another related question: Assume that the number of websites over the internet remains same over the time (static) and anti-phishing tool company A knows the set of legitimate websites $S$ and illegitimate websites $S'$. Is it possible to prevent phishing by distinguishing the set $S$ from the set $S'$, for example by blacklisting the sites in $S'$ or by allowing connection only to sites in $S$?