Hi, I seem to be having the same problem though it's not on a flash drive but on my system. I downloaded a free program that was supposed to help me extract mulitple files at once and the installer also added some adware and I believe that could be the problem but of course, I'm not an expert. I've run avast twice, once in the boot-time scan and it found Win32:Installer-U [PUP], but I didn't let it finish...oops. I ran a full system scan and it found Win32:Dropper-gen [Drp]. Looking at it now, it looks like it also found Malware from one of the "offers" that was installed with the program.
Here are the file locations:
Uninstall.exe - C:\ProgramFiles\Uninstaller\Uninstall.exe - Win32:Installer-U [PUP]
Custom.dll - C:\ProgramData\InstallMate\{99853496-E169-4392-A179-A94B42661660}\Custom.dll - Win32:Dropper-gen [Drp]
ExtensionUpdaterService.exe - C:\ProgramFiles\V-bates - FileRepMetagen [Malware]
I moved the Win32:Installer-U and Win32:Dropper-gen to the chest.
I scanned with OTL but it only left an OTL.txt log file. It is attached.
