Hi Martin,

On 4 December 2016 at 18:29, Martin Urbanec <martin.urbanec@wikimedia.cz> wrote:
I was running weblinkchecker.py for whole cswiki (job was submited to the grid at Sun, 20 Nov 2016 16:54:24 GMT) because I wished to have a list of deadlinks. This may correspond with the UA (because I used script named weblinkschecker.py). I trusted this script it won't do anything wrong because this script was and still is in standard core package. I also use 3.0-dev version of pywikibot and Python 2.7.6. 

It probably wasn't you, but it was indeed the standard weblinkchecker causing this. Apparently no throttling is implemented -- just a maximum number of parallel connections. Many parallel connections are fine... but not to the same host. This bot was running on eswiki, and ewsiki has thousands of links to http://www.minorplanetcenter.net/.

I have contacted the user, and will file a bug for Pywikibot to get this solved on that end.