Avast causing 100% disk usage

Since last week my disk has been at 100%, mostly caused by avast which I subscribe to. How do I make it stop?

  • Which Avast…? (Free/Premium)
  • Which version/build of Avast…?
  • OS…? (32/64 Bit…? - which SP/Build…?)
  • Other security related software installed…?
  • Which AV(s) did you use before Avast…?