When the site was suspended, I was advised to use a reCatchpa instead of the question and answer as a means of preventing unwanted members.
It soon became apparent that this was not a good idea so I have gone back to the Q&A system which requires prospective members to have some knowledge about Links.
There will always be the odd occasion when someone slips through the net but as soon as they post anything inappropriate I de-activate them.
I am 99.9% certain that you cannot get a virus just be browsing the forum, reading and answering posts. The only thing you need to be wary of is clicking on external links, but this applies wherever you are on the internet these days.
It is when you click on links or download files where you are likely to get into trouble.
Obviously have decent Anti-virus software running and up-to-date and be wary of where you download files from and from who. The best protection is what you do yourself, or really don't do.
I think the Links specific question makes more sense and would likely restrict the people who can sign up. reCAPTCHA is more about stopping automated signups. Of course you can always put in more humps and have both :)
For what it's worth all forms of social media have been infiltrated by trolls.
Look at Facebook...it statlrted with posts about Spr8ngsteen and Deniro moving to Canada. Now it's a weird headline linking to some advertising...it's happening every day...and people respond...go figure.
My advice-if it passes itself off as "news" but you don't recognize the poster just check with a "trusted" site (some might call it "fake news" but...)