PUP.Optional.Multiplug refers to a type of browser hijacker that intercepts the connection between the browser and the Internet using “file-in-the-middle” tactics to push advertisements to the user. This Potentially Unwanted Program (PUP) may also redirect browsers to different start pages and search browsers in order to monetize the user’s browsing.
More modern versions of this threat are called Dotdo.
Common infection method
The most common method if infection by this threat is through bundled software.
Malwarebytes removes this threat. However, there may be some leftovers you might need to clean up.