Network security protects computer systems and networks from hackers and mistakes. It involves designing secure network infrastructures, policies, and rules as well as continuously monitoring security measures. Files can be made publicly shareable or protected and shared only with authorized users as determined by file owners or network administrators. Firewalls filter incoming internet information to private networks using software or hardware, allowing only authorized traffic according to security policies. Digital signatures authenticate messages and documents by using a private key to sign them and a public key for verification.