Which protocol should be block to prevent malicious attacks?

To prevent malicious attacks, blocking unnecessary or vulnerable protocols such as Telnet, FTP, and SMB can be effective. Telnet and FTP transmit data in plaintext, making them susceptible to eavesdropping and interception. Additionally, blocking unnecessary services like SMB can help mitigate risks associated with ransomware and other exploits targeting file-sharing vulnerabilities. Always use secure alternatives like SSH and SFTP for remote access and file transfers.