Hello Beth,

They're probably Brown Marmorated Stink Bugs, though any number of species which overwinter as adults may be inside as well. They won't hurt anything, and are just a nuisance as they wander about or try to head back outside now that the days are lengthening and warming. They came inside in autumn or during mild spells in winter, and like any insect that wanders in for shelter, keeping them out is relatively simple and involves sealing any access points. Gaps/cracks on exterior walls can be caulked and any door or window weather-stripping (and torn window screening) can be replaced. Some night-active insects can be attracted to outdoor lighting at night (like porch lights), which may give them easier access to accidentally wandering indoors when the door is opened or if weather-stripping has gaps that they find while walking around.

Miri