The phrase "unwelcome intruder" means someone or something that is not wanted or invited, but still enters or comes into a place or situation. Full definition
This new piece of jargon has rapidly entered the military lexicon, with commanders and technologists alike talking about the «human terrain» to describe the interaction of culture, groups, and people that can, for example, lead to military forces being treated either as liberators or as unwelcome intruders. (discovermagazine.com)
Split perspectives between and within the families illustrate mounting tensions as the McAllans treat the Jacksons as the help, if not unwelcome intruders. (slantmagazine.com)
A related problem is the misunderstanding of their legitimate roles; because guard dogs are trained to neutralize unwelcome intruders, many people mistakenly believe that Dobermans are vicious. (sheppardsoftware.com)