wordpress95 on "WP_POSTMETA data increasing massively."

Hi

I have some problem with my database.

http://i.imgur.com/f4kxLug.png

Suddenly, WP_POSTMETA increasing massively on meta_value column with the same data(“IjwhRE9DVFlQRS~”) over 100mb per day.

First time, i just deleted it.

But, When i disabled all my plug-ins and themes for checking the problem, it still made every single time. I couldn't find this problem in google.

Why it happened? how can i solve it?

Thanks.