I was hacked! What to do?

Question

ubuntu

Installed Ubuntu 14.04.3.
Today I discovered that they changed passwords for all users and set a password for root (root was blocked).
Of course, I removed the password from root, and changed the password for other users.
No one has physical access to the car except me.
I installed programs only from the repository (except for VirtualBox, which is from the site).
Used the latest Opera with ad blockers.
What to do next?

Answer 1

The system is compromised, there is zero trust in it. Reinstall! And review the security policy. If the machine is directly connected to the Internet, the first thing to do is to configure iptables, fail2ban.
However, everything is a little more than strange. Follow the simplest rules of network hygiene and you will be happy.

Answer 2

and they also say that windows is full of holes... format

Answer 3

Today I discovered that they changed passwords for all users

Have you changed the layout, is capslock enabled?
PS I'm sorry I couldn't resist.