Nobody mentioned hackers. Script Kiddies, was the meter.

There is no reason to include admincp and modcp in robots.txt. The bad bots are going there anyway.

Particularly, you don't want to include your admin and mod directories if you've changed them for the very reason vBulletin let's you change them in the first place. To make it harder for a hacker to guess where they are.

But as an aside, it's pointless to put them in robots.txt, since, as was mentioned, robots.txt is an honor system thing. Legitimate bots already know about and have no use for your Admin CP (presuming the name hasn't been changed.) Whereas bad bots aren't going to honor it in the first place. Robots.txt is something you use to control how much legitimate bots see and index. Don't even consider it for bad bots. For bad bots, consider other blocking tools such as Simon's modification or .htaccess. In my case, my host let's me ban IP addresses from all my domains via cPanel, which simply automates the editing of .htaccess across all my domains.

For robots.txt, you may want to try a little trial and error. A few years ago I was getting slammed by MSNbot. I didn't know why (probably because Bing was about to startup in a year or two), but it was hogging system resources and was exacerbating pre-existing conditions. So I set a crawl-delay for MSN.

[pre]User-agent: msnbot
Crawl-delay: 3[/pre]

Basically, I'm saying you tweak robots.txt according to your needs. Look at your modifications that have their own unique pages. Do you feel the need to have it index every one of those? Just as an example, if you had iTrader installed, you probably wouldn't need the iTrader ratings page indexed. Or the arcade. Or a page devoted to Facebook login. You probably have default pages that don't need to be indexed, like login.php or private.php. Robot.txt will help to keep bots from wasting their time there.

That's some good info, thanks.