A teergrube (German for tar pit) is a computer server set up to be intentionally slow, as a trap for spammers using address harvesting programs. The owner of the teergrube sets out fake e-mail addresses in places where harvesting programs search, along with a human-readable warning not to send messages to those addresses. The address harvester, unable to read the warning, collects the addresses and the spammer duly sends spam. The spammer's messages are accepted by the teergrube, albeit very, very slowly, thus tying up resources. A teergrube is configured to maintain a Simple Mail Transfer Protocol (SMTP) session for exceptionally long periods -- sometimes more than 24 hours -- so that the session is not timed-out. The extended time period that a spammer is stuck in a teergrube may also afford more opportunity to detect the source of messages.