Pascal's mugging refers to an apparent paradox in decision theory, named in analogy to Pascal's wager. An agent with an unbounded utility function that uses Solomonoff induction to assign probabilities can potentially be exploited by bets offering tiny probabilities of vast utilities: describable utilities get large must faster than the the probabilities given by the Solomonoff prior get small. The situation is dramatized by a mugger:
Now suppose someone comes to me and says, "Give me five dollars, or I'll use my magic powers from outside the Matrix to run a Turing machine that simulates and kills 3^^^^3 [in Knuth up-arrow notation] people."
Intuitively, one is not inclined to acquiesce to the mugger's demands, and yet it's not clear how this intuition can be justified in decision theory.
"Pascal's Mugging: Tiny Probabilities of Vast Utilities" by Eliezer Yudkowsky
"Pascal's Mugging" (PDF) by Nick Bostrom. A dialogue of the scenario in Analysis