Blumofe Robert

Form 4 filings are required within two business days of any insider transaction by an officer, director, or 10%+ shareholder. Open-market purchases (transaction code P) are the most signal-rich because they indicate the insider is paying market price with personal cash — as distinct from option exercises, scheduled sales, or compensation grants. Cluster buying — three or more insiders of the same company buying open-market shares in a 30-day window — has historically been one of the strongest positive insider-trading signals in the academic literature.