Try to restore it and see if the restore fails.
Restore HeaderOnly only looks at the header, so only if the header is damaged will it give any indication. Restore VerifyOnly doesn't verify the entire backup, unless the backup was made WITH 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