1. A method of passing validated information along a series of entities, the series of entities including a source entity, a plurality of intermediate entities, and a target entity, wherein each of the entities shares a validation parameter with its immediately neighbouring entity or entities in the series, the method comprising the steps of: (a) in the source entity, generating a validation code for the information, the validation code being based on the validation parameter shared between the source entity and an intermediate entity of the plurality of intermediate entities; (b) outputting the validation code; (c) receiving the validation code in the intermediate entity and making that intermediate entity a current entity; (d) verifying the information via the validation code in the current entity using the validation parameter required to verify it; (e) in the current entity, generating a validation code for the information, the validation code being based on the validation parameter shared between the current entity and a next entity in the series; (f) outputting the validation code; (g) receiving the validation code in the next entity in the series and making that entity the current entity; (h) verifying the information via the validation code in the current entity using the validation parameter required to verify it; and (j) repeating steps (e) to (h) until the current entity in steps (g) and (h) is the target entity, wherein the next entity in the series in steps (e) to (g) includes at least another intermediate entity of the plurality of intermediate entities, and non-valid information is periodically passed to the target entity and whether the non-valid information is valid or non-valid is verified in the target entity.