Where does “hakkaantua” come from?

hakkaantua (Finnish) comes from Finnish -Vntua, from Finnish -untua, from Finnish -ntua, from Finnish -ua, from Proto-Finnic -üdäk — Forms mainly passive or anticausative verbs.

Ancestry of “hakkaantua”, step by step

Step	Language	Word	Meaning
1	Finnish	-Vntua	Forms passive verbs
2	Finnish	-untua	—
3	Finnish	-ntua	Forms reflexive or inchoative intransitive verbs
4	Finnish	-ua	Forms stative or inchoative intransitive verbs...
5	Proto-Finnic	-üdäk	Forms mainly passive or anticausative verbs

Every word from Proto-Finnic -üdäk →Every word from Finnish -ua →Every word from Finnish -Vntua →