How to tell if web visitor is a robot

Question

On an ASP website, is there a way to tell whether a visitor is a robot?

I'm thinking there might be a parameter in the ServerVariables collection that could be used, in a similar way to HTTP_X_FORWARDED_FOR and REMOTE_ADDR can be used to get the visitor's IP addresses.

Searches on Google have so far yieled few leads.

Answer 1

My suggestion would be to try

HTTP_USER_AGENT

Answer 2

There is no bullet-proof method because headers and origins can be spoofed.

Answer 3

if a visitor access robots.txt it's most likely a spider. IF there is nothing in the host or user-agent information or there is no referring URL or IP address changes within a visit or if the log lines appear together in an uninterrupted block in the log file then it's most likely robot traffic.

thanks