There is no rundll16 file existing under Windows. It should be a Virus or other kind of Malware. You should reinstall Avast or use a other onlinescanner to see if there still is some malware left.
A list of online virusscanner can you find here: http://www.bul-online.de/av/onlinescan.html
RAV or Mcafee are good ones.

Maybe cleaning te mouse is a good option too!:slight_smile: