strange files in my upload_tmp_dir

Hello, I should probably know the answer to this but I do not. I was hoping someone here could offer me some incite. I recently changed my upload_tmp_dir from the apache default; actually it wasn't set at all, to another directory which I created for this purpose. The directory is outside of the normally accessible directory structure for apache web on my Linux box. I have no forms anywhere on the site which allow FTP just yet. I manually uploaded a few files and have been downloading them via a local VB program. So no PHP access to the directory yet. Today I noticed about 20 files, all named something like php??????. They are from various time during the day and have a zero file length with no content at all. I have no idea where these files are coming from. They are certainly not session files as those are appearing correctly in another directory. Any ideas on what these might be? Thanks very much! Gerard Onorato