For substantial reward (in particular, is one of the manifestations of modern competition ) , etc. NOTE The most dangerous types of viruses are now considered worms and » Trojans «. First able in a short time spread over a local network , while the latter are implemented in a computer and can do basically anything — depending on what purpose they were created ( theft of information , disabling hardware or software , and so d ) . To protect against computer viruses on the computer have to be good anti-virus program installed . There are many such programs , among the most famous may be noted Kaspersky Anti-Virus (www.kaspersky.ru), Avast (www.avast.com), Dr. Web (www.drweb.com), NOD 32 (www.esetnod32.ru), Norton Antivirus (www.symantec.com), etc. It is not enough just to install a program on your computer — you also need to monitor the relevance of anti-virus and update them in a timely manner . Note that in most modern antivirus programs implemented the ability to automatically update antivirus databases . This is the most convenient option , because the update process proceeds without user intervention , and runs automatically as needed. Do not forget that for automatic updating , you must have an active Internet connection . spyware The main difference between spyware Spyware from computer viruses is that they usually do not harm the software and data stored in the computer ( except for the fact that they are distracted by a certain amount of system resources and hard disk space ) . Problem of spyware is to collect some user information ( email address , the contents of the hard drive , list of visited web pages, personal information , etc.) and send it to a specific address . The user does not even know that he was under some kind of secret surveillance . Information obtained in this manner can be used in a wide variety of purposes, which can be relatively harmless (analysis of the attendance or other sites ) , and very dangerous (for example, if the information obtained will be used for unlawful purposes or to the detriment of the user ) .