What kind of spam is this?

[ljhelbo]

During the last few days my server gets bombarded - this is from apache access log:

41.252.246.153 - - [18/Sep/2013:23:02:55 +0200] "POST / HTTP/1.1" 200 1733
93.141.82.13 - - [18/Sep/2013:23:02:55 +0200] "POST / HTTP/1.1" 200 1719
41.108.3.204 - - [18/Sep/2013:23:02:55 +0200] "POST / HTTP/1.1" 200 1716
80.57.29.93 - - [18/Sep/2013:23:02:55 +0200] "POST / HTTP/1.1" 200 1717
186.113.42.60 - - [18/Sep/2013:23:02:55 +0200] "POST / HTTP/1.1" 200 1732
76.208.204.10 - - [18/Sep/2013:23:02:55 +0200] "POST / HTTP/1.1" 200 1716
76.208.204.10 - - [18/Sep/2013:23:02:55 +0200] "POST / HTTP/1.1" 200 1715
93.64.141.2 - - [18/Sep/2013:23:02:55 +0200] "POST / HTTP/1.1" 200 1716
85.43.254.153 - - [18/Sep/2013:23:02:08 +0200] "POST / HTTP/1.1" 200 13459
87.30.218.178 - - [18/Sep/2013:23:02:57 +0200] "POST / HTTP/1.1" 200 1717
47.65.9.239 - - [18/Sep/2013:23:02:58 +0200] "POST / HTTP/1.1" 200 1728
80.101.119.13 - - [18/Sep/2013:23:02:58 +0200] "POST / HTTP/1.1" 200 1728
217.141.30.190 - - [18/Sep/2013:23:02:58 +0200] "POST / HTTP/1.1" 200 1736
81.149.177.44 - - [18/Sep/2013:23:02:58 +0200] "POST / HTTP/1.1" 200 1736
193.205.8.164 - - [18/Sep/2013:23:02:58 +0200] "POST / HTTP/1.1" 200 1735
82.207.122.202 - - [18/Sep/2013:23:02:58 +0200] "POST / HTTP/1.1" 200 1716
37.207.253.178 - - [18/Sep/2013:23:03:42 +0200] "POST / HTTP/1.1" 200 1356

The server has turned pretty slow because of this. The main problem is however that I do not understand the purpose of it. I presume somebody must be trying to achieve something, but what and why?

[ljhelbo]

I have come a little further by now. I have found out which domain, they were bombarding. I have now renamed the www-folder with the files for that domain. Now my apache_error.log has a long liste with "file does not exist". But at least all other domains now run as they should.

On the domain, which they are trying to attack, there is a Pivotx-installation and an installation of webtrees. Over the weekend, I will try to rebuild them fom scratch and then see, if I can trace the reason.