It's not about security. Checksum page protection lets SQL pick up more forms of corruption than Torn page could, and also can show that said corruption is caused outside of SQL.
There's a very small overhead in having it on, I think it's around a 2% hit. Personally I'd say that every SQL 2005+ database should have page protection set to checksum.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability