Final answer:
The most effective way to prevent a virus from infecting your system after copying a file from an infected CD is to use antivirus software, keep it updated, and employ sandboxing techniques.
Step-by-step explanation:
If you copy a file from a CD that is infected with a virus, the most effective way to prevent the virus from infecting your system is to use a reliable antivirus software.
Antivirus software scans files for viruses and removes any threats before they can infect your computer. Additionally, it is important to keep the antivirus software up to date to ensure it can detect and protect against the latest viruses.
Another way to prevent the virus from infecting your system is to use a sandboxing technique. A sandbox is a virtual environment that isolates the copied file from the rest of your system. By running the file in a sandbox, any malicious actions performed by the virus will only affect the sandboxed environment, protecting your actual system.
Lastly, always exercise caution when copying files from an infected CD. Check the files for any suspicious behavior or unexpected changes in file size, and avoid running any executable files without first scanning them with antivirus software.