Vista - 127.0.0.1 localhost entry missing from hosts files

Hi,
I've come across several Vista machines where the following entry is missing from the hosts file.

127.0.0.1 localhost

On most machines it has both the IPv4 and IPv6 loopback addresses, i.e.
127.0.0.1 localhost
::1 localhost

however on some I've seen that it only has the IPv6 loopback address
::1 localhost

This is affecting how our application runs. Does anyone know if this chagne was done as part of a Windows security update or is this a change that Antivirus software commonly makes?

Many thanks,
Eoin

Hi,
I've found the following posts that suggest that a Microsoft Defender update was the cause.
Known Issues in Installation, Configuration, and Deployment
Alex York .NET | Windows Defender deleted localhost entry in hosts file - UPDATE

Unfortunately, Microsoft don't categorically state that this update deleted this entry. Can someone from Microsoft confirm that this was the case?

Thanks,
Eoin

I doubt you'll get anyone from Microsoft actually looking in here, but doing a Google search on the matter, it seems that WD has been guilty of removing the local host at various times in the past.

This article for instance from last March: Martin Falatic’s Techno Blog » Blog Archive » Windows Defender apparent false alarm (Win32/PossibleHostsFileHijack)

As Windows Updates have free online suppport why don't you ask them directly?