I don't think a captcha to post would make a difference if it's a human spammer that already got past the captcha to make an account on the forum, in the first place.
I don't think we have an issue with spambots reviving old threads. If anything, it's human spammers that are quite capable of passing a captcha test, clicking extra buttons, etc., so adding more hoops for humans to jump through in order to stop spammers would be pointless, as they can jump through the same hoops anyone else can.
Restricting posting on older threads only to members after a certain number of posts is also not such a good idea, as this would deter posting to an older thread by someone that actually has something valid to add that may have just discovered the forum.
The best we can probably do with regards to human spammers posting on old threads is to delete it when we catch it and ban the spammer.
But it might be easier to spot if there was a visual indicator to readers, like I explained before.
Another thing to keep in mind is how I detect spam on the forum is usually with popup cody
. If I see something that is obvious spam, I click through and take action, usually before anyone else gets a chance to see it. And I am not the only one that uses this method and is removing spam. (that's why you don't see that much spam around here) There is nothing in the popup to indicate when the last post in the thread was, so I don't know when I see it that an old thread was just revived. I do have an indicator of when the thread was started, but that really isn't anything to go by on this forum because there are many threads that have had a long beautiful life and still going strong. (the note-taking thread
, for example)
If you do see something you suspect is spam, report it. I check all the reports that hit my inbox and delete any obvious spam, and if I am not sure about it, I leave it to another mod to check or bring it to mouser's attention and ask him what he thinks.
All in all, this forum has very little in the way of a spam problem. And it has been kept well under control. You can read the RSS feed from here without seeing a million spam posts, unlike another forum I am a member of, in which their feed is so loaded with spam (about 90%) that I can't find the valid posts any more. I had to unsubscribe and go back to visiting that forum directly, in order to avoid the spam. (google reader caches the posts in the RSS feed and shows older stuff that was removed, which includes all the spam) DC's RSS feed is still very clean in google reader, which means we are doing a great job getting rid of it very quickly.
We are not being over-run by spammers, so relax. This isn't an urgent issue that needs drastic action that would inconvenience normal members.