PUP.MultiSearchBox is a name of malware that explains major features of the program at once. PUP stands for “potentially unwanted programs”. MultiSearchBOX is thus the name of program one might find unwanted.
It is to be noted that antivirus products flag the detection for other potentially unwanted programs. Basically, the detection name is used to mark some of adwares of StartSearch hijacker family.
Remove PUP.MultiSearchBox and use genuine search tools e,g. Google. Free scanner available here is recommended PUP.MultiSearchBox removal tool.