Swastikas appear on my desktop background screen

I recently have found that I have a background screen
filled with small swastikas. I don't know how they got
there, and I don't know how to get rid of them.

Control Panel - Display - Background - (none) but what
shows up is a black background with tiny swastikas.

Any body got any ideas. For example, what is the name of
the file that is used to create "None" on the desktop
background.

Thanks

Lowell