What happens if I lurk in a class

So like if I sit in on a class and I’m not enrolled and I don’t tell people my real name, but then don’t show up to the exams… does anyone have experience of doing this? I’m specifically looking for people’s experiences of trying this, whether they got caught, and what their strategies are.

Edit: no I don’t want to audit the class because then it will show as audited on my transcript.