Unfortunately I did not find much info because, if I understand, the ransomware blocks all operations to reset your TV using the remote control.
Anyway you can try a factory reset by following this guide
Where are you seeing this fake alert ..within the browser or it's everywhere? A picture would help...
Did you tried to disconnect from the Internet and unplug the TV? Also I would reset the router to its default settings!
Do not send any money to these cyber criminals as this is just a scam!
The environment of a Smart TV should not infect easily since the part of executing a program is different than from Desktop and Laptop + only recognized preinstalled program are able to execute well, I think you should follow the advice by @Jack.
Your case seems extremely strange. Does the problem persist across reboots?
Mandiant is an actual company, and accordingly there is no information of any sort that they have just undertaken such an operation.
Meanwhile, several ransom ware families are using its name to hold user's PCs ransom. However, LG TVs run on a linux based OS, and I don't think there is any ransom ware disguising as Mandiant on the linux platform yet.
Off topic: Imagine a world where medical devices start becoming "smart" and ransom wares can literally hold your life ransom
Below is the message we are getting on our LG google tv.(I do not have the screen shot with me as it is on my spouse's phone.) We get the message as soon as we power on the tv, regardless of how it is turned on. I believe it it first popped up after my spouse was waiting for the system update to load. We have unplugged it waited and plugged it back in, that didn't fix it. We have not rebooted because we could not get anywhere on the tv. We will follow the reboot guidelines posted within this thread tonight and see how it goes. We called LG support and they told us it was not possible to have this happen. We sent a screenshot to them and they said hmmm..... we'll get a tech on it. Thank you to all who have responded and I am anxious to get home and see if this reboot works. I'll let you know.
Thank you all so much for your input. We followed some advice in this thread and were able to factory reset. All is working and family is happy. I am so, so glad I found this site, the LG tech was going to charge $250.00 to come out and do ehat I'm sure would be the same thing we were able to do ourselves. Again, thank you to everyone who commented on this post.