Leaked password or hacked pc?
I use multiple Proton and Gmail accounts across different websites (I’m not saying the email accounts themselves were hacked).
Recently, I noticed unauthorized logins on several services: LinkedIn (Gmail), Instagram (Proton Mail), Twitter/X (Proton Mail), and most recently Reddit (Gmail).
Some of these services detected the logins and sent me security emails, but in other cases I didn’t receive any notification about a new login or session.
What makes this especially concerning is Reddit, since I use Google Sign-In and have 2FA enabled, so it shouldn’t be possible to access the account with just a leaked password.
What could be causing this? This seems like more than just a password leak, especially since multiple unrelated accounts using different email providers are being affected.
Could this be caused by a malicious Opera browser extension, stolen session cookies, malware, or even a keylogger on Windows?
How can I systematically detect which of these possibilities is responsible?