Free antivirus programs like AVIRA (http://www.avira.com/ru/) are updated automatically and do not require a charge. Their disadvantages in the absence of some features such as phishing filter, but for home use such programs fit perfect. You also at anytime can upgrade to the paid version (or try it for thirty days).
If you are using a paid antivirus program, then its extension will mean buying a new package. This is usually done once a year. Antiviruses are sold in computer stores and also online. For example, on the website http://www.kaspersky.ru you can buy or renew a subscription to such a program.
Sometimes to renew your subscription, you'll need to buy a new package, but only special cards which will contain an activation code. The cost of renewing the license for a year is usually equal to the present value of the annual license, minus forty percent. With this kind of discount is extended only packages that are designed for a period of not less than six months. These rules apply to the antivirus program firms "virus" that NOD32 and Doctor Web.
You can use the kindness of those users who have purchased packages activation and decided to share codes on the web. To do this, go to the website http://tfile.ru/forum in the search bar at the top of the page, enter the word "keys" and among the results, select your option antivirus program.
Sometimes the license renewal cannot be carried out in connection with an outdated version of the program. For example, if you installed the 2003 version, you will have to purchase a new, later model year.
Remember that buying a license of the antivirus program gives you much more protection for your computer and information stored on it.