Very hard to say... theoretically you should be able to use your ledger on an infected pc and still not lose your funds...
I can think off a couple very remote scenario's that happened, or were at least discussed in the past:
- You saved your seed in the cloud, and your account got hacked (icloud, dropbox, gmail,...)
- You saved your seed on a physical carrier, and somebody found said carrier
- You entered your seed in a different (vulnerable) wallet
- You were the victim of a clipboard virus (eventough, this would have required you to actually make a transaction)
- You received a device that had been tampered with... either preloaded with a seed, or plain fake
- You were the victim of an evil maid attack (somebody had physical access to your device)
From all of these suggested possibilities, I do admit I saved the seed in my google drive. To access my gmail account though, requires 2FA. Google did not notify me for a remote login etc. I used the same seed since 2017 on the same ledger device.