I scanned my three computers with MalwareBytes and NOD32 but no viruses / malware were found.
My email account that was used to send SPAM had the same password since 2015. As a security measure I will change the passwords of all mail accounts I have on heliohost.
All my accounts are set up within a GMAIL account. I do not use desktop mail clients (Outlook, Thunderbird, etc.). I still do not understand how they could have obtained my password.
Another thing: I understand that heliohost limits 50 outgoing e-mails per day, which for my use is more than enough. How is it possible that the spammer was allowed to send thousands of emails in a matter of hours without being blocked?
I await your comments. Thank you very much.