Taiwan's biggest maker of IC substrates is under a criminal search, a negative shock for the company and its shareholders.

• Prosecutors searched Unimicron, the leading supplier of the boards that carry advanced chips.
• The company said the probe centers on a dispute over where its products are labeled as made.
• Its general manager, a vice president and other staff were taken in to cooperate with the investigation.
• Market chatter goes further, pointing to faked books, insider trading and disguising the origin of goods to get around US rules — claims the company has not confirmed.
• Unimicron has now put out two separate disclosures on the same day, a sign of how fast the story is moving.

Outlook: The company says it will issue another statement once prosecutors formally explain the case, and the shares are likely to stay under pressure until then.