Is my site being attacked?

Hello all,
    Today, I cannot access my site. I asked The Host provider to check the server. They said that I seem that your site is being attacked & ask me to check configuration of my site. 

I'm using CodeIgniter 3.0, My site has being worked since last year, It's no problem. However, today, I checked on the host, a lot of files were generated, I don't know why (Please see attachment images)
It seems that my site is being attacked by some one.

I don't have much experience with CodeIgniter. Is there anycode that generated these files? How can I prevent this? (I'm using DEFAULTS CONFIGURATION of CodeIgniter3.0). 

Could you help me please?

BIG Thanks for your helper!

Regards,
Tuan

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