My error-log show hacking attempts. Should I be worried?

Most of my blogs were hijacked recently and their traffic was being diverted to other sites. I have done my best to resolve the problem, and some of the lost traffic has come back now…

Today, I checked my error log and was shocked to see strange things in them… Looks like hacking attempts are ongoing, or probably have even succeeded. How should I rescue my sites?

Here is an example of stuff in my error log — https://pastebin.com/8PqNJgw9

So, does it look like I have been hacked? How should I rescue my blog?