bogus files not spotted by Avast

Hello:
I have the latest free version of Avast (just installed it) but don’t know the version number. I am using win 8.1 in a Lenovo computer. I recently discovered that some mystery files are being inserted into my computer by the dozens and these mystery files are extremely large so the hard drive was almost filled up!
Here is what I found by using an app called WinDirStat:
the mystery files look like this: 12754694899610736661_2853498758043839360_4480_4480 ~ 960 MB
ver1
they are sent to this location in my computer: C:$Recycle.Bin\S-1-5-21-2712117882-3860235528-2112810399-1002

When I open the mystery file in FIREFOX it looks like this:
file:///C:/recyclebin/12754694899610736661_2853498758043835520_3840_3840
which is an application/octet-stream (960 MB) from C:\recyclebin

Note: file opens in Firefox but there is no information in the page and, after selecting Ctl - U, there is NO code at all!

These files are still coming into my computer after installng Avast so PLEASE help me if you can. I can catch these files with the help of WinDirStat but want to stop them altogether. I believe a virus has invaded my PC and had hoped that Avast would catch and kill it.
Thanks,
jim

Please follow the instructions : https://forum.avast.com/index.php?topic=53253.0

Have you emptied your recycle bin ?