To improve computer security, use complex passwords, change passwords on a regular basis, and install antivirus programs. Additionally, don't open emails from unknown sources; if you receive a suspicious email, especially one that has an attachment, delete the email, and make sure to delete it from the "deleted items" file.
Complex passwords are difficult to crack. To make your passwords strong, use a combination of uppercase letters, lowercase letters, numbers and symbols. If possible, use different passwords for different websites. Be sure to install only one antivirus program in your computer, as installing more than one lowers the performance of the computer. Keep the antivirus program up to date.
To safeguard your computer from Internet-based threats, install at least one firewall. Hardware-based firewalls are more effective than software-based firewalls, as they act as the only point of entry. They are also more flexible and customizable. To reduce chances of infection, don't share your hard drive with strangers, and check your operating system to see what users have access to your hard drive.
Regularly back up your data in case of a security breach. If possible, store your backups offline. If your computer has programs that you rarely or never use, uninstall them. Evaluate the settings of software already installed in your computer, especially those that have access to the Internet.