Adware

Adware is a type of software which is typically classified as a "Potentially unwanted program." Adware displays advertisements on a user's computer, smartphone, or other such device. Some adware also includes spyware—it tracks device usage to deliver targeted advertisements. Adware is typically installed without the user's intentional consent. It is often bundled with legitimate software, so the failure to uncheck a box or select some other small option permits the installation. In some cases, it is instead forced onto the device using malware such as a trojan or worm. However, in some rare cases, a user voluntarily and intentionally installs it. In some cases, they do so because they like the (often targeted) advertisements, while in other cases they are paid or given some other form of compensation for using it.

Adware is considered malware by most, and as such, is sometimes guarded against by anti-virus software. There are also programs which are more focused on non-virus malware, like Ad-Aware and Spybot which will try to block and/or remove this presumably unwanted software. Even if the adware package itself it safe, the advertisements loaded by it can be potentially infected without the adware publisher's knowledge.