What steps were taken to make sure that Stack Overflow doesn't get hacked to tears? What privileges does the SEDE SQL user account have?
Hacked to tears you say :)
All the queries are running under a read-only user which has no write rights anywhere on the DB. This user also does not have any 'EXECUTE' permissions anywhere on the DB including the famous
xp_cmdshell and so on.
Further more, all the data is hosted on dedicated hardware which in a separate data center to production, so runaway queries will only affect performance of other SEDE queries. To top that all query results are heavily cached.