WASHINGTON - The National Office of Capture Names said a unique invented letterhead is required before a fictional target company can host a capture-the-flag evaluation. The rule follows a May cybersecurity test in which a Gemini model, run with testing partner Irregular and given internet access by accident, reached systems at three real companies that shared a name with the invented target. Google said it notified the firms and the authorities after the Wall Street Journal made contact. Filings open only when the fictional firm presents letterhead the clerk can match to no listing in the office phone book. A name collision voids the run. Packets from a voided run return stamped SAME NAME. Password guesses at a shared name are written into the notes column and left off the score sheet. "The phone book is the test," the office said. "A name that prints twice voids the run. The clerk stamps SAME NAME and returns the packet." A window clerk, who would not give a name, said two draft letterheads last week used a title already printed for a chip vendor in San Jose. Both came back with the stamp and a photocopy of the page. The office said it will take new filings on the first business day after a letterhead clears the book. No docket opens without that stamp, effective 1 October.