Malwarebytes should fix it. However, scan through the registry and look for any entries containing the word(s) 'MS Juan.' Also, make sure any and all programs you don't know are deleted. Common entries in the registry are:
HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main\Active State
HKEY_CURRENT_USER SoftwareMicrosoftWindows CurrentVersionRunOnce*WinLogon
HKEY_LOCAL_MACHINE SoftwareMicrosoftWindows CurrentVersionRunOnce*[filename]
HKEY_CLASSES_ROOTCLSID{2316230A-C89C-4BCC-95C2-66659AC7A775}
HKEY_CLASSES_ROOTCLSID{8109AF33-6949-4833-8881-43DCC232B7B2}
HKEY_LOCAL_MACHINE SOFTWAREClassesATLEvents.ATLEvents
HKEY_LOCAL_MACHINE SOFTWAREClassesATLEvents.ATLEvents.1
HKEY_LOCAL_MACHINE SOFTWAREClassesCLSID{02F96FB7-8AF6-439B-B7BA-2F952F9E4800}
HKEY_LOCAL_MACHINE SOFTWAREMicrosoftWindows CurrentVersionExplorerBrowser Helper Objects{02F96FB7-8AF6-439B-B7BA-2F952F9E4800}
HKEY_LOCAL_MACHINE SOFTWAREMicrosoftWindows CurrentVersionExplorerBrowser Helper Objects{2316230A-C89C-4BCC-95C2-66659AC7A775}
HKEY_LOCAL_MACHINE SOFTWAREMicrosoftWindows CurrentVersionExplorerBrowser Helper Objects{8109AF33-6949-4833-8881-43DCC232B7B2}
HKEY_CURRENT_USER SoftwareMicrosoftInternet ExplorerMainActive State
Hope it helps.
