I have some advices, hope it can help.
Do you use free hosting service? I ever used free hosting service, they inject ads into my database. Now I won't use any cheap or free hosting services. A good and reliable web hosting usually is not cheap.
The computer you're using can be the source of the problem too. I mean if you're sharing the computer with others especially in internet cafe, you're risking your password being stolen. Do you save your passwords on the computer? It is risky, anyone can easy get the passwords if you're using Firefox. Also you need to make sure the computer is virus free. I personally use Linux.
This Better WP Security is great, it really blocks and reduces the hacking attempts on my sites. You may need to consider manually ban the IPs who are frequently visit and try to hack your site.
For useless bots (spambots) I also use Bad Behavior plugin. From the logs, I can see it really blocks a lot of bad visits.
For improve the security further, you may also install these plugin:
- Login Security Solution
- BulletProof Security