Most tests and experts claim that while antivirus software is extremely useful in preventing some cyber attacks, it is unable to prevent all attacks. That's because once a piece of malware has been identified, hackers know that this malware will be added to the list of already-known viruses, and it will no longer be able to pass through most signature-based detection systems. Also, antivirus software is not perfect, and there are constantly new and emerging threats that frequently bypass a computer's defenses.