[deleted] Hi there, and thank you for your enquiry. As a user, you only see a small part of the spam filtering on this forum. Therefore, allow me to give you a little insight into how it works.
We use a spam filter, which blocks the vast majority of spam. The posts get automatically deleted by the spam filter, and their accounts are suspended.
I believe your enquiry may have been prompted by an increase in the number of spam bots bypassing the spam filter within the last 48-72 hours. The issue with the spam filter that caused that has now been fixed, and the amount of spam has subsequently decreased again. We apologize for the increase in spam over that timeframe, and would like to reassure you that this issue that caused this has now been resolved.
Occasionally spam bots comment on old threads, usually because the thread contains a string which matches one of those keyphrases. In addition to deleting the spam and banning the spam bot, we tend to lock those threads too. That's because once one spam bot tries to use that thread, the likelihood of another using it afterwards increases. We prefer to take this cautious approach.
If you require that thread to be unlocked, you can always create a new thread asking for the locked thread to be unlocked, and we can look into that for you. Please do let me know if there are any specific threads you require to be unlocked.
With the spam filter working as normal, the vast majority of spam is blocked, and old threads are very seldom locked. For that reason we are not currently considering using Captcha.
I hope that helps to answer your query. Should you have any further questions, please don't hesitate to ask.