Thought this might be interesting as ive tried searching for people who have had a similar experience but i found nothing that seems to match my exact findings.
Running J-tag with 12611.
Ive never blocked my jtag box from the internet on my router but did have it so i would never connect to live.
I normally never have my j-tag connected to my network unless im copying files over to the box.
Ive never had any issues until last week. For some reason i left it connected for a few days and the kids turned it on and played with it for a few days.
I noticed later everything seemed fine but when i unlocked an achievment on my profile it destroyed my profile. What was strange it did not show up as 'corrupt' as the profile still loads. It just show up with 0gs and no games played. Also when restarted i have to assign my avatar again, but when finished it says there is a problem and never saves it. Unflagging and rehashing does not fix it. The profile is now totally destroyed.
A bit of looking around it seems all the profiles on the j-tag (live and non live) that were not created on the j-tag suffer the same issue. They are not corrupt but if you unlock any GS the profile gets wiped. All profiles that were created on the j-tag are fine.
So it seems MS can now silently ban/blacklist your box and after doing this will make your profile unrepairable.
The only way to fix the issue was to reflash the NAND and restore a old backup of my profile. Lucky i had a backup of my profile from 2.5 months ago so i anly lost about 8000GS.
Anyway the moral to the story is block internet access to your jtag (use the latest dashlaunch) as MS can silently set your box up to destroy yourprofile.
Anyone experience anything similar? Just be careful and make plenty of frequent backups of your profile.