from wikipedia:
In Utero was mastered by Bob Ludwig at Gateway Mastering in Portland, Maine. According to Azerrad, apart from the minor modifications to "Heart-Shaped Box" and "All Apologies" (with Scott Litt), the rest of album was left as it was recorded, and all that was done at the final mastering stage was to sharpen up the bass and boost the vocals by 3 decibels.
so there.
also, i've read interviews with albini where he claims that it is impossible that any of the versions floating around on the internets are 'his' version.
but i take it all with a pinch of salt. it's my favourite album for reasons above and beyond simple aesthetic pleasure..