To counter sniffer attacks, using encrypted protocols for all communications ensures that even if data is intercepted, it cannot be read without decryption. Additionally, using switches instead of hubs improves security because switches provide a direct communication path between the sender and the receiver, minimizing the risk of data being intercepted by an unauthorized party. Reducing the range of a network is not a reliable countermeasure for sniffer attacks as it does not address the core issue of data interception. Furthermore, tools like StackGuard and Immunix System are not specifically designed to prevent sniffer attacks; they are more suited to preventing buffer overflow attacks.