Another website with such an alert: -breckle-direktverkauf.de/ → https://urlquery.net/report/1117058e-f610-41e9-b9da-51da54258faf
See DNS MX issues: https://threatintelligenceplatform.com/report/breckle-direktverkauf.de/JnGihV8qjN
F-Grade status and recommended change: https://observatory.mozilla.org/analyze.html?host=breckle-direktverkauf.de
redirecting to -http://www.osterburgmatratzen.de/
1 vuln. libarary: http://retire.insecurity.today/#!/scan/2d7f11fe4fa2c647d8a2523422825778090a04c233dc5aa1b1989bbd9ecdb934
Also consider IDS alerts: http://urlquery.net/report/d0c77fe1-b155-43cc-8a8b-39712139d283
Also consider sources and sinks here: http://www.domxssscanner.com/scan?url=http%3A%2F%2Fbreckle-direktverkauf.de
Read: https://github.com/jquery/jquery/issues/2432
Same origin upheld but issues resulting in a B-Grade scan result: https://sritest.io/#report/e588fc78-dc4c-4e6f-916f-e365e6093ad1

Error

found JavaScript
error: undefined variable jQuery
error: undefined function t
inside: wXw.osterburgmatratzen.de/wp-content/plugins/yith-woocommerce-compare/assets/js/jquery.colorbox-min.js?ver=1.4.21

As errors in the theme code

ound JavaScript
error: undefined variable jQuery
error: undefined variable f.fn
error: line:1: SyntaxError: missing ; before statement:
error: line:1: var f.fn = 1;
error: line:1: …^
inside: wXw.osterburgmatratzen.de/wp-content/plugins/revslider/public/assets/js/jquery.themepunch.tools.min.js?ver=5.4.5.1 (110418 bytes, 48 hidden)

polonus (volunteer website security analyst and website error-hunter)