In the past few days, several of my accounts on different apps/websites (first Twitter, then Discord) have gotten hacked, posting messages and sending spam messages to my contacts without my knowledge. As soon as I noticed this was happening, the security on these websites kicked in, blocking my account, and I was able to immediately reset my passwords, which seemed to do the trick.
However, now I got another "attack", this time on my Gmail accounts, that I use to login to Twitter, Discord, and dozens of other websites. I started receiving hundreds of "Mail Delivery Subsystem" spam emails. I immediately also changed passwords to both emails, and blocked the senders, but I am not sure what I should do to protect myself from other attacks.
I access my email accounts on all my devices - on my laptop (Windows 10 OS), and my phones (I have an Android and a work iPhone) - and through Google Chrome. Neither of them have any additional security software, other than the built-in security on both devices. I assumed the security breach would be on my computer, since it accesses more websites, but after running deep security scans with Windows Defender tools over the last few days, no threats were found.
Since this all happened in the span of a few days, I want to take action I can as fast as I can, but I am not sure where to start. Does anyone have any recommendations on what I could right now with the build-in security tools of Google Chroe and what type of security software I should use to run diagnostics on my devices and protect my accounts (particularly, on my computer)?