Choice "A" is correct. The protective device that keeps Internet users from accessing intranet data is termed a firewall.
Choice "b" is incorrect. Anti-virus protection programs scan computers for viruses and, in some cases, destroy them but do not provide security from external access to an organization's private data.
Choice "d" is incorrect. A browser is a software mechanism that allows for research on the Internet or intranet. It is not a security measure.
Choice "c" is incorrect. A password provides security regarding internal access to information but is not a comprehensive security device or procedure to prevent access to a computer system and its data.