I experienced the same while traveling in Bali.  Was trying to provide feedback on a thread I had started asking about use of VF roaming in Bali (VF prepaid account).  Just wanted to confirm it was working well (- except, as I found out, I was never able to post on GZ.  Well not on that thread, did not attempt to start a new topic). 

Oh, meant to add that I was attempting to post from my mobile phone (Galaxy S8).  And that I was able to login in to GZ fine.  No VPN! 

I have New Zealand whitelisted and the security level at low for most other countries. This is managed at CDN level and should only really show a CAPTCHA for the worst cases - IP addresses that have been recently flagged as "bad actor", automated browsers, etc.

Since this is done at the network level, I can't bypass it with 2FA and so on.

neb: I didn't get a CAPTCHA, I got redirected to the forum index and a message about IP-based blocking from Thailand, Slovakia, and the Czech Republic. From Austria it's OK.

 

Ah, yes. In this case it is an anti-spam protection we have in place. I've Trusted your account so you should be able to post from everywhere now.

Happened again here:

https://www.geekzone.co.nz/forums.asp?forumid=48&topicid=190840&page_no=547#2326463

I posted that then realised i'd copy-pasted the address from the wrong browser tab so edited then link and got bounced back out after the captcha.  Posted another immedate reply with the correct link, this worked.  Copied the content from my first post, pasted it into the second which was fine.  Deleted the original and no captchas.

*shrug*

And now I am getting this problem posting from home here in Auckland (for the uninitiated, yes part of white-listed NZ).

Posting from my desktop PC.  Forum is "LAN (ethernet/Wifi/routers/Bluetooth)" - new thread.  Not certain that is the correct forum - post relates to a options for a video intercom system - network and SIP phone options discussed.

Browser is Chrome, ISP is Vodafone (VDSL).

Post contains three web links (one to PB Tech, and two to Fanvil Hong Kong website - just regular commercial websites).

Attempting to post brings up the page below.  And, yes I have scanned for viruses.

https://www.geekzone.co.nz/forums.asp

Oh, meant to say, clicking on the captcha redirects to the forum index.

Interestingly, my post just now re the problem went through without any such issues.

Possibly only 'New Topic' posts affected?