Final answer:
To prevent virus infections from USB flash drives, disabling the autorun feature is the most effective measure. Strong passwords, password protected screen savers, and disabling the guest account are general security measures that do not specifically address USB drive infections.
Step-by-step explanation:
To prevent virus infections from USB flash drives, one should disable the autorun feature. Autorun is a feature that automatically runs a program when a USB flash drive is inserted into a computer. Disabling this feature can prevent viruses from spreading through the USB drive.
Strong passwords and password protected screen savers are security measures that can protect the overall security of a computer system, but they do not specifically prevent virus infections from USB drives.
Disabling the guest account is also a security measure, but it does not directly address virus infections from USB drives.