Malware
Malware (a portmanteau for malicious software) is any software intentionally designed to cause damage to a computer, server, client, or computer network. Malware does the damage after it is implanted or introduced in some way into a target's computer and can take the form of executable code, scripts, active content, and other software. The code is described as computer viruses, worms, Trojan horses, ransomware, spyware, adware, and scareware, among other terms. Malware has a malicious intent, acting against the interest of the computer user—and so does not include software that causes unintentional harm due to some deficiency, which is typically described as a software bug.
Malvertising
Malvertising is a fairly new concept for spreading malware and is even harder to combat because it can work its way into a webpage and spread through a system unknowingly: "The interesting thing about infections delivered through malvertising is that it does not require any user action (like clicking) to compromise the system and it does not exploit any vulnerabilities on the website or the server it is hosted from... infections delivered through malvertising silently travel through Web page advertisements." It is able to expose millions of users to malware, even the most cautious, and is growing rapidly: "In 2012, it was estimated nearly 10 billion ad impressions were compromised by malvertising." Attackers have a very wide reach and are able to deliver these attacks easily through advertisement networks. Companies and websites have had difficulty diminishing the number of malvertising attacks, which "suggests that this attack vector isn’t likely to disappear soon."