Website hacked through DB

Hello my website was hacked, every day I found mallware on my website.
In Slow query log on my webhosting reports I spoted something strange

# Time: 160212 23:17:22
# User@Host: 5ptppav7[5ptppav7] @ [10.10.35.15]
# Thread_id: 63641660 Schema: 5ptppav7 QC_hit: No
# Query_time: 5.231082 Lock_time: 0.000046 Rows_sent: 0 Rows_examined: 15697
use 5ptppav7;
SET timestamp=1455315442;
SELECT * FROM wp_options WHERE option_value REGEXP ‘(QGV4dHJhY3QoJF9SRVFVRVNUKTs|CQk8TUVUQSBodHRwLWVxdWl2PSJyZWZyZXNoIiBjb250ZW50PSIwO3tmcmFtZV91cmx9Ij4K|NjMuMjQzLjEyOC0yNTUuKg==|aWYoIWlzX3VzZXJfbG9nZ2VkX2luKCkpeyAKCglpZihpc3NldCgkX0NPT0tJRVsnd3BzZXNzaW9uJ10pKSByZXR1cm47CglpZihpc19hZG1pbigpKSByZXR1cm47CglpZihmdW5)’;

How can I prevent it?