What's the worst virus you've ever had on your PC?

[Riberet19]

Many viruses can infect and damage your PC, there are Trojans, keyloggers, worms, ransomware,e and some others, in your case what has been the worst virus you have ever had and how did you solve it?

In my case, the worst has been a Trojan, I installed a software I thought was benign and damaged my PC when I ran it.

 

[Nomad]

I once had trojon virus on my laptop. I lost all files on my C drive. Sad part was I had not backed up my laptop for a couple of weeks and the best part was my disk was partitioned and I only lost files on C drive.