Network security consists of the provisions made in an underlying computer network infrastructure, policies adopted by the network administrator to protect the network and the network-accessible resources from unauthorized access and the effectiveness (or lack) of these measures combined together.

Computer Security is a branch of information security applied to both theoretical and actual computer systems. Computer security is a branch of computer science
that addresses enforcement of ''secure'' behavior on the operation of
computers. The definition of ''secure'' varies by application, and is
typically defined implicitly or explicitly by a security policy .

Comparison:

Securing network infrastructure is like securing possible entry points of attacks on a country by deploying appropriate defense. Computer security is more like providing means of self-defense
to each individual citizen of the country. The former is better and
practical to protect the civilians from getting exposed to the attacks.
The preventive measures attempt to secure the access to individual
computers--the network itself--thereby protecting the computers and
other shared resources such as printers, network-attached storage
connected by the network. Attacks could be stopped at their entry
points before they spread. As opposed to this, in computer security the
measures taken are focused on securing individual computer hosts. A
computer host whose security is compromised is likely to infect other
hosts connected to a potentially unsecured network. A computer host''s
security is vulnerable to users with higher access privileges to those
hosts.