To put it quite simply, no it can't block every virus every time. There stands a pretty good chance that as long as there are viruses, anti-virus software programs will continue to need updates. The technology to overcome this problem is considered non-existent and unavailable as long as computers exist. The reason for this is quite simple when you think about it. Most of the programs we use on our computers are software based, such as anti-virus protection programs. All of these programs are written in computer language called codes or definitions. Each new program requires a new code. Each new code can be useful or malicious depending on the computer programmer that essentially authors the code for a specific purpose.
That is the primary reason anti-virus software cannot keep up with virus inventors. Modern day anti-virus programs use blacklisting technology to store malicious code from known viruses; they are incapable of predicting what a future virus code might look like. Some anti-virus software companies have begun using heuristic algorithms in their products in an attempt to create a sort of virus prediction process, in which the security system might be able to identify similar virus patterns from an established database and use that information to stop incoming or outgoing traffic that meets a certain criteria. Although this might be helpful to some people, it can pose a problem for other users. Any unregistered or unknown incoming source has the potential of being blocked if the program fails to recognize the requesting websites authenticity.
In reality this is how protected your computer is. Let's say you knew somebody that had the knowledge and necessary equipment, including software to create a computer virus, and let’s just say for the sake of argument the two of you were sitting next to each other, on separate computer systems, laptops for instance. You could receive a notification from your anti-virus provider that you had updates available that need to be downloaded and installed. As you are going through this process, your computer programming associate is putting the final touches on a virus they have been creating. You complete the process of downloading and installing the necessary updates and rebooting the computer so the new updates take effect. Your friend at the same time wraps up their virus in a neat little email attachment and sends it to you. You open the email click on the attachment and before you know what happened your computer crashes. You're probably going to be extremely upset and probably even furious with the anti-virus software company for the product you are using.
It isn't their fault the virus corrupted your computer; the malicious code the computer programmer attached to the email had not been discovered and added to the update yet. Compounding the problem is the fact that you used poor judgment when you opened the email attachment even though it came from a trusted friend. Most of us don't have friends that would do that to us, not intentionally anyway; however this example proves a point about the problem of assuming simple anti-virus protection is sufficient for providing your computer with enough security.
Good Internet habits, proper anti-virus software procedures and perhaps the addition of an Intrusion Protection Program are all key ingredients to establishing the best possible solution for your computer's security. Keeping all of these software applications up-to-date and current is also highly recommended since a program that doesn't have the latest updates will be even more ineffective against viruses and result in increased exposure to unknown virus definitions or the malicious codes that they use.