realscanner.dll is a dynamically linked library that is installed and used by WistaAntivirus. It's another rogue anti-spyware, which seeks to steal people's money by warning them about invented viruses. Once it scares them, it offers buying its fake license and promises that it will fix their computers. In reality, WistaAntivirus is the one that should be eliminated from the system. Otherwise, it may start causing slow downs, displaying tons of annoying ads and redirecting your browsers to unsafe websites. For avoiding that you should remove WistaAntivirus with all its components.
realscanner.dll is an essential component of WistaAntivirus. In most of the cases, it is responsible for launching this threat, so basically it wouldn't work without realscanner.dll. However, this file can also be responsible for other activities and work on its own.
NOTE! realscanner.dll file may also be a fully legitimate part of the operating system or legitimate software. No matter that such cases are really rare, you should carefully check this file before deleting it. For that we recommend using RegCure Pro.