PandaViewer is classified as a PUP and a browser hijacker. It is downloaded to the computer by either being downloaded or bundled with free-to-download programs from freeware websites like download.com and softonic.com.
The program injects tracking cookies into the user's browser and collects the user's search data. Most times after the program is downloaded, PandaViewer will try to push the user to changing their homepage to Search.PandaViewer.com, which is more than likely just a modified Google search page. It also can change web pages to make them display an excessive amount of Panda Viewer ads.
This program also increases the CPU utilization to nearly 100%, making the system slower and potentially more vulnerable.