What are the possible and most dangerous effects of computer Viruses in compoter systems and websites?

Computer viruses are programmed to harm your computer by damaging programs, deleting files, or reformatting the hard drive. Others simply replicate themselves or flood a network with traffic, making it impossible to perform any internet activity. Even less harmful computer viruses can significantly disrupt your system’s performance, sapping computer memory and causing frequent computer crashes.

References:
https://www.webroot.com/in/en/resources/tips-articles/computer-security-threats-computer-viruses