Malvertising involves cybercriminals inserting malicious code into online advertisements to infect visitors without clicking. The malware can slow devices, record keystrokes, and encrypt files. Ad networks unknowingly distribute the malicious ads to viewers. When a page loads the ad, the malware downloads and finds a backdoor to install onto the device. People can protect themselves by keeping browsers and plugins updated, using adblock software, limiting downloads, and adjusting browser settings.