I had the same issue. I generally keep my PC up to date with all updates needed being done automatically.
I use the client version.
Same date, 17th of Feb, I also had the same problem when windows defender flagged the ClientPatcher.exe as a Trojan and naturally, it quarantined the file and 4 other files associated with the game.
I did as it asked and did a full scan of my PC using windows and it found nothing.
I told it to delete the affected files from quarantine.
I couldn’t use either of these to access the game
But I could use this to open the client with
These are located in the “Secret World Legends” folder on my PC.
I then selected the option to “Repair Broken Data” from the options tab
Once it finished, I then created new shortcuts for my desktop and was able to access the game again.
I can’t guarantee it will last as I don’t know if it could be flagged as a trojan again, but it hasn’t as yet and its been 2 days now.
And I can’t guarantee that this works for everyone, or how this works for Steam versions - just what has worked for me.
Hopefully things get sorted soon from Microsoft so it doesn’t happen again.