is avast's Filtering NDIS driver.
From what you describe it appears part of the uninstallation process has become corrputed. I recommend you reinstall avast, reboot to verify it is working, then reboot in safe mode and try uninstalling again.
Anti-virus software components insert themselves deep into the operating systems core where they install kernel mode drivers
that load at boot-up and create files/folders/registry entries in various locations. It is not uncommon for some anti-virus programs to not completely uninstall itself using the usual method of Programs and Features
or Add/Remove Programs
in Control Panel due to the presence of related services and processes running in the background. Sometimes the uninstall works more effectively if you first stop and disable the program's service
(and associated processes) or perform the removal in safe mode
so there are less processes which can interfere with the uninstallation.