i need help

i want the best rule to prevent network virus
my mikrotik version is 3.3
and thanks in advance

The best rule is deny all xD very good question.. Please, reread your question and say with me: WTF?!

i couldnt understand
my question is about that some virus in network computers affect the performance of the internet and make alot of “request timed out”
are there some codes in mikrotik that would prevent this effection on the internet ??