Where to purchase anti virus ?

Would you kindly discuss if there are some managers of the system which will be connected to the internet that can limit or eliminate some damage which are done by worm or virus.
If there is a system for that, may we know where can we find and purchase it.
Can you tell us, what are the advantages and disadvantages of having this system.
Please, I really need the complete information and advised.
Thank you so much.
