Aliens different form us…?

If they look so "biologically different from us"- assuming that we know what every species of creature on this planet looks like, and has metabolisms and behavioral patterns that we recognize - we should see them as nothing but aliens. Then, again - and to repeat a popular science fiction trope - they might just be walking, eating, farting and sleeping amongst us (not fornicating and reproducing with us, successfully, at least, because it is entirely unlikely that even though they might look like us, their DNA will be a replica of ours. But who knows? If they look like species among us, they've probably got to gene splicing, perhaps gene replication, perhaps even gene creation - in which case, they are us. Perhaps the alien is a virus in my laptop that's found a way to jump the binary-gene barrier and has leaked into me through my fingertips and is forcing me to write this crud. Man, this is a complicated business. I'd better degauss my laptop. Better to lose all my software than to turn into an alien virus hatchery.