Please help. Unwanted "Microsoft Picture It" download box

I have a weird problem. When I access some trusted sites
(one is the Pacman's Portal startups site), and type in
data in their search box, a download box sometimes appears
asking if I want to save a file for "Microsoft Picture
It". The problem is that I did not request a download at
all, and I don't use Microsoft Picture It. I click on the
X to get rid of it. What could be causing this? I
regularly scan my computer for viruses and spyware but
find nothing. Thank you for any comments, etc.