Corroborative evidence is evidence which supports a theory that was deduced from initial evidence (either direct or indirect, best, or a copy). This evidence is used to confirm the proposition, or as a backup plan if the initial evidence is challenged. Corroborative evidence in the case of the rain example would be a second person coming in wet, or the local weather forecaster saying that rain is currently falling.

These bits of evidence support the direct evidence given by the man (the man's statement) and the indirect evidence given by the clothing and umbrella. The following diagram demonstrates an extended rain example, complete with corroboration, direct, and indirect evidence examples. The TV weather forecast is indirect, because the forecast is generically about the area, rather than the localized, specifically-outside-your-office weather. This would be different if it was an outside broadcast and the reporter happened to be outside your office:

Corroborative evidence in a ransomware attack might be that the attacker was seen meeting the co-conspirators and receiving cash, along with communications discussing the attack and subsequent money collection. Neither the meeting, nor the communications, are direct evidence – it can be easily argued that the discussions were hypothetical and that the cash was unrelated – but both events do support the other evidence, thus linking the attack to the money and the attackers.