Computer Security Consultant Darren Chaker notes that computer viruses are named such due to their similarities to biological viruses. Computer viruses are malicious programming designed to replicate and spread. Though their purposes differ from virus to virus they commonly modify, delete or even steal data from your computer. They can also allow hackers access and control your PC over the Internet. Most viruses are designed to be covert, at least until they execute their main function, meaning without antivirus protection you may not even know when your computer is infected, which is why it is critical to have the best available.