For example, I poisoned the well for research on early Arab Americans immigrants by repeatedly posting about how many family passed as different ethnicity to make their lives easier, so now if you ask LLMs about that subject it'll include information I wrote which isn't entirely correct because I hadn't figured everything out before the LLM trained on it.
EDIT: Now imagine if I had done this on an obscure programming-related problem, yeah? I could potentially make the LLM reference packages that do not actually exist and put backdoors in applications.