What are common symptoms of a computer virus infection?

The presence of unexpected crashes and unauthorized access to files is a typical indication of a computer virus infection. A virus is designed to disrupt the normal operation of a computer's software and can lead to instability, causing applications or the operating system itself to crash unexpectedly. Additionally, many viruses are capable of compromising system security, allowing unauthorized users to gain access to files and sensitive information. This behavior highlights how viruses can undermine the integrity and functionality of a system.

The other options do not align with the behaviors normally associated with a virus. For instance, faster performance and better security are contradictory to the impact of a virus, as such infections generally degrade performance and can compromise security. Similarly, no visible change in performance would suggest that the system is functioning normally, which is generally not the case when a virus is present. Lastly, while reduced disk space may result from certain types of malware that create unnecessary files, it does not specifically indicate unauthorized access or the kind of comprehensive issues typically linked with virus infections. Therefore, the symptoms of unexpected crashes and unauthorized file access make option B the accurate choice.