Computer virus - Term used in computer security to describe small piece of software, which abuses user's computer and data without his permission or knowledge. Viruses were mainly damaging the data in the past. Modern virus are trying to conceal their activities far as possible and, completely without the user's knowledge, misuseing his computer for various illegal activities (attacks on other computers, sending spam, stealing data, ..).

Trojan horse / Trojan - Program that appears to perform a desirable function (usually useful or funny), but in fact its main purpose is to install a virus to computer of the user who launched it. In itself its not a virus but represents a major threat anyway.

Anti-virus - Software which is able to detect viruses in your computer using several different techniques. It uses a database of samples of viruses that need to be constantly updated to be able to find newly created viruses.

JavaScript - Scripting language, which is often used on web site. It allows web pages to be dynamic right in your browser so they may offer a very useful or effective tools. Most modern viruses, which are spreading via web pages, are using JavaScript for infecting computers.

HTML / XHTML - Simple language which is used for creating web pages.

IFrame - Element (tag, 'command') of HTML and XHTML languages, which allows inserting of one HTML document into another HTML document. Many modern viruses are using it in their spreading.