[One (M8) Q&A, Help & Troubleshooting] redpoint73:
You won't find the Euro "401" ROMs on that webpage. I don't think they were ever "officially" released by HTC, but there are leaks of some of the official RUUs around (such as the Marshmallow one I linked you to).

Let me look around, and see if I can find the Euro Kitkat RUU.

Again, I'm not sure this will help or not. It's impossible to be sure, since we don't even know what your friend flashed. But I think at this point, it's worth trying.

---------- Post added at 09:52 AM ---------- Previous post was at 09:37 AM ----------

RUU = ROM Update Utility

This is a HTC-proprietary recovery or update tool, which installs a complete "stock" factory image (all partitions on the phone). RUU will fix a lot of problems related to software/firmware.

We've seen some instance where flashing the wrong radio to some versions of the M8 (radio brick) can be fixed by flashing an older (Kitkat) RUU. But I don't think I've seen this work specifically on the Euro M8 or not. But like I said, it's worth a try.

It's actually a bit complicated. Normally, where it says "cidnum" on the getvar output will tell you the CID (carrier ID) number, which you can use to determine the carrier version. But in your case, it's been modified by the previous owner/seller to be "SuperCID" (11111111) which bypasses any CID check.

Where it says "modelid", this is the Model ID or MID. The MID of 0P61B10000 would indicate the device is one of a number of European versions. The product name (m8_ul) would also indicate this (although that product name is also used for some other versions). The version-main number (which indicates the firmware or OS number) 6.12.401.4 would indicate the unbranded Euro version, with the number "401" being specific to the Euro unbranded M8.

Now, all those properties (CID, MID, OS number) can be modified with s-off. Except product ID (m8_ul) which I've never seen modified. So it's possible it was some other version which shared the product name of m8_ul (branded Euro versions, Australia, US T-Mobile). But the preponderance of the evidence would indicate the phone is the unbranded Euro version.

That is all very confusing, I know. And I only know this from hanging out in this device forum section since 2014. The important thing, is that this is setup as an unbranded Euro device right now. So probably easiest to just leave it that way for now, as we try to troubleshoot the "no network" issue.

---------- Post added at 09:58 AM ---------- Previous post was at 09:52 AM ----------

S-on/off is an HTC specific measure, also called "security off" which basically means that you have access to certain "protected" partitions which are usually can't be user-modified with s-on (which s-on is the default factory condition).

You can do some useful things with s-off, such as change the CID and MID, and "downgrade" to an older RUU (not possible with s-on). It was used to make it SuperCID (11111111) which is often done to remove carrier SIM lock.

But on the other hand, s-off leaves the device open to damage from flashing the wrong things. In particular, when a person that doesn't know what they are doing, it's possible they can flash a file (radio, ROM, etc.) intended for some other device, and that can damage the partitions on the phone. I have a strong feeling, that is what happened in your case with you friend.