The act by a user of posting in such a way that the forum software crashes; i.e. "He hammoed the forum."
The term originates from a mis-post of code to the ski.com.au forums by use 'hammo' which took the forums offline. Hammo in fact posted no code and did nothing untoward, but had the misfortune to be the last, or one of the last, posters immediately before a major crash. That evil bastard Ian S, who has since been cast out into the farther darkness for other sins against peace and order, coined the expression, which stuck.