Modifiers matching intruder:

• nonhuman,
• harmful,
• unwanted,
• outside,
• pesky,

Simple categories matching unwanted:

• portion,
• pest,
• item,
• larva,
• herbivore,
• condition,
• friend,
• software,
• material,
• conduct,
• parasite,
• organism,
• elements,
• fluid,
• contaminant,
• feeder,
• user,
• insect,
• game,
• information,
• substance,
• papers,
• medium,
• liquid,
• adulterant,
• artefact,
• behavior,
• animal,
• compound,
• communication,
• light,
• literature,
• microbe,
• content,
• surface,
• particle,
• folder,
• growth,
• signal,
• situation,
• germ,
• residue,
• filler,
• bacteria,
• thing,
• document,
• stain,
• action,
• message,
• body,
• sediment,
• grub,
• layer,
• event,
• reaction,
• ingredient,
• emotion,
• target,
• nuisance,
• input,
• file,
• protein,
• plant,
• instrument,
• hair,
• happening,
• medication,
• comment,
• byproduct,
• trait,
• child,
• object,
• effluent,
• panel,
• chemical,
• place,
• pesticide,
• nonsense,
• cell,
• sound,
• spam,
• tree,
• consequence,
• illumination,
• process,
• thought,
• reptile,
• activity,
• shade,
• creature,
• pollutant,
• advert,
• email,
• solicitation,
• noise,
• movement,
• program,
• intermediate,
• molecule,
• solute,
• response,
• container,
• atom,
• fuel,
• stuff,
• debris,
• energy,
• odor,
• souvenir,
• rodent,
• odour,
• view,
• behaviour,
• entity,
• phenomenon,
• scavenger,
• state,
• critter,
• extra,
• trace,
• treasure,
• acceleration,
• fabric,
• soil,
• effect,
• agent,
• impurity,
• occurrence,
• infection,
• constituent,
• furniture,
• equipment,
• ion,
• symptom,
• person,
• vegetation,
• interference,
• variable,
• matter,
• article,
• advertisement,
• species,
• part,
• space,
• deposit,
• emission,
• mammal,
• incident,
• blemish,
• grass,
• variation,
• waste,
• intruder,
• branch,
• bird,
• solid,
• gas,
• motion,
• bedfellow,
• yeast,
• metal,
• artifact,
• code,
• disturbance,
• pet,
• coating,
• mineral,
• intrusion,
• volatile,
• entrant,
• structure,
• people,
• acid,
• particulate,
• predator,
• component,
• substrate,
• mail,
• contamination,
• feature,
• caller,
• change,
• textile,
• appliance,
• tissue,
• microorganism,
• piece,
• vermin,
• area,
• inhabitant,
• fungus,
• fish,
• smell,
• hardwood,