Downloads have _ instead of . for extensions

I have had several computers get this problem. When downloading and you get the run, save, cancel option at the bottom you can't click on run, and if you look at the file downloading it will have a _ where the . should be. This has happened on various sites, even trying to install adobe flash player and java on a fresh install of windows. Sometimes it won't let me save or cancel the download and I have to close the browser. Most of the time I have to restart the computer for it to work correctly. If you do get the file to save, rather than open you can change the (example) flash_exe to flash.exe and it will run correctly. Any suggestions would be appreciated.

I don't think it is a virus. I had a new build computer that I just installed windows on. The only thing other than installing windows was I installed all windows updates. After the computer rebooted from that the first thing I did was start to install adobe flash player. When it popped up the open, save, cancel box it was like this. Went ahead and hit save and changed it once it downloaded so I could install it. Maybe its some windows update that causes this. I just started getting this maybe within the last month. Guess I should go back to not installing windows updates.

I will try that and see what happens. Will probably be a few days before I know if this makes a difference. I kinda think one of the computers that did it still had 10 on it, but I can't be certain.