111-222-1933email@adress.tst hacker

111-222-1933email@adress.tst hacker

I am learning website languages, and i am still a beginner. I am building
a website that uses registrations, logins, adds, and so on... First I used
PDO in my php in order to prevent mysql injections. Anyway I was hacked,
they did not delete the database but it is full of this e-mail
111-222-1933email@adress.tst, and a strange code. I think that they used
acunetix to see the leaks of mine website.
My question is: Do you know whats he hacker did, and what measures
(besides PDO) can i use in my website to have a little bit more of
security?
Thank You