Unknown URLs

Hi!

My statistics show some external domains which have nothing to do with my site.
E.g.

I track my Domain: example.com

My statistics show something like:
example.com
|_ index.html
|_ site2.html

external.com

How can this happen? Can anybody use the tracking code for my site and embed it in his own?

see external requests show up in statistics · Issue #8551 · matomo-org/piwik · GitHub