People were unknowingly accepting Lightning bitcoins that weren't actually backed by real bitcoins. These people wouldn't even find out until they went to withdraw their coins from the Lightning Network (i.e., close the channel). 1/2
Lightning Network vulnerability disclosure: CVE-2019-12998 CVE-2019-12999 CVE-2019-13000 Update your nodes if you haven't already!
You can find 's original disclosure mailing post here
ICYMI: Here are all the details of the recent Lightning bug.
This is why we shouldnt let money unsounders near our money: should have used the real BTC. :(