I tried to download a particular exe file using Firefox (found here: http://www.gpsfiledepot.com/maps/files/1-3394-aztopo_install.exe), but each attempt failed according to Firefox. I found that in my Downloads folder, trzXXXX.tmp files of the correct size were being saved (where XXXX is random characters). I downloaded the exe file without difficulty on another computer, but when I transferred the exe file to my problem computer, it changed names to trz231B.tmp when I attempted to run it or copy it. On the problem computer, I am able to download other exe files without them changing names. Renaming the tmp files mentioned above so their extension becomes exe results in the extension reverting to tmp when attempting to run them. (When downloaded locally, the name changes to the trzXXX.tmp before attempting to run it, but this does not happen on the other computer. Several other files at the same site download normally on the problem computer.)
I have Avast on the computer, and I also ran a scan with it, but there were no relevant findings. I downloaded and installed MalwareBytes Anti-Malware, and there were no findings related to this problem. I also downloaded and installed TDSSKiller, and no problems were detected.
As it stands, I am unable to run this one exe file but everything else seems normal.
Thanks in advance.