Strange behavior when saving a file

I'm using Illustrator 10.0.3, Mac OS 10.2.8.

When I make changes to one of my Illustrator files and save it, it makes a copy of that file to the same folder where it exists on my desktop. The file is saved as a number, 135174, and the date modified seems to be either the date when I copied it from a zip disk or made a copy of it from the original (but I don't exactly recall this detail). Either way, the date modified doesn't reflect the present date.

What is this?

Thanks.