Looking for an advanced blur filter

[Dot50Cal]

Hi guys, I searched the forum but I cant find anything related to what I need. Basically I need to blur only small portions of a video and only for a selected amount of time (approx 5 seconds). Does anyone know of a filter which can accomplish this?

[Manao]

It would be doable with avisynth. With Virtual Dub, it would require a specific filter, which I think doesn't exist.