To keep a desktop computer secure on a company's network, I start by ensuring that the system is joined to the company's domain, which helps in managing security policies centrally. Next, I install and regularly update antivirus software to protect against malware and other threats. I also disable USB ports to prevent unauthorized data transfers via external devices. Additionally, I configure user permissions carefully, ensuring that employees have access only to the resources necessary for their roles. This minimizes the risk of accidental or intentional data breaches. Regularly updating the operating system and all installed software is also crucial to protect against vulnerabilities. Finally, I educate users on best practices for network security, such as recognizing phishing attempts and using strong passwords.