Hi,
just visited the following website hxtp://stadt-bremerhaven.de/ which is actually trustworthy. During page load, I got a malware notification by avast (see attachment). I wonder, if it’s a false positive or if I should restore my PC with a backup, since there may have been other undetected malware, which came together with this attack.
The blocked url definitely belongs to the RedKit Exploit Kit so there was some kind of redirection on your site or on the site you link to (advert for example).
I can’t verify where the redirection was fired from - its probably replaced by the backup. However I would suggest checking your website security.