Are there any web-application-firewall level spambot filtering that would ensure that the bot traffic can be continually monitored and the rules to block spambots can be continually updated?
Simplicity is the ultimate sophistication.
Therefore, just to offer a counterpoint, I would like to register my experience here. A random name surely did not do the trick for us. Simple tricks like creating a random hidden field would be broken by spambots in less than 48 hours. It took a great deal of expensive WAFs like Barracuda and a lot of Lua scripting combined with cookie analysis (and overall request header analysis) to detect spambots with only a 90%-95% accuracy and keep them out.
Most of the spambots jsut search for forms to fill on the internet.