Little sniff configuration for system process

Please, what is the best configuration for Little Sniff protection in Leopard (OX 5.8) ?

Once the user does not share with other computers, neither uses icloud, iDsik or MobileMe ?

In other words, what should I definetely let come in so as to keep my connection and data safe, but still update well my system & softwares automatically?

By the way, what's Pub Sub Agent role, besides RSS updates?

thanks any & every help.