Malware is a short for malicious software. Usually, this term describes a wide range of programs that can harm your computer. Malware includes viruses, Trojans, spyware, etc.
Typically, cyber criminals are spreading Malware disguised as a useful software. They can create fake video sharing sites that look like YouTube. Then this website asks user to install plugin or codec for viewing video.
Be careful when web site requires the installation of plug-ins, extra programs, etc! To protect yourself from Malware use antiviruses. We also recommend Microsoft Malicious Software Removal Tool.