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Octomom must live next to a bunch of 49ers fans -- because when she arrived home after watching the Super Bowl at a friend's house ... she discovered one of her window's had been SMASHED!

Sources close to Octomom -- real name Nadya Suleman -- tell TMZ, Octo and her 14 children had spent Super Bowl weekend at a friend's place ... and weren't home from Saturday afternoon to Sunday midnight, so the vandal(s) had nearly 36 hours to attack.

As soon as she noticed the damage, we're told Octo called Palmdale Police ... who showed up 15 minutes later to take pics of the damage ... and make sure no one was lurking inside (the place was empty).

As for whodunit ... sources close to Octo say she has a hunch it's the same person who's allegedly been harassing her and the kids for months now.

We're told this incident is the final straw -- and now, Octo's having an alarm installed ... soon as the window's fixed ... with stripper money.