I've just scanned bitcointalk.org

http://sitecheck.sucuri.net/scanner/ - Clean

https://www.virustotal.com/en/url/7354af8427d7b8d4236356d0bca680ad3186fce415cb51971f3793cee59e4291/analysis/1385144339/ - Clean

However, I found that hpHosts is currently listing bitcointalk.org - i.e. 'Malwarebytes'.

See: http://hosts-file.net/?s=bitcointalk.org this is probably an error and the admin. should contact 'Request removal' for more info.

Not 100% sure how ads are being served here, but it might be to do with temporarily hijacked 3rd party content and/or in relation to linked content.

This report, I suspect is actually a 'false positive'.