Due to a security issue we've disabled SSL 3.0 on our servers.
Ninite uses the HTTP client built into Windows and that depends on the version of Internet Explorer that is installed and its settings. Even if you use a different browser, the IE version and its settings matter.
First, make sure you're using at least IE 7 or later. Earlier versions do not have support for TLS. If you're still using IE 6 you can upgrade in Windows Update.
Next confirm that TLS is enabled in Internet Explorer's settings. Microsoft has good instructions for doing this.
Once IE is set to use TLS Ninite will begin working again. If you keep having trouble there's probably another problem. Please get in touch with us and we'll help you.
We were mitigating this issue with TLS_FALLBACK_SCSV shortly after the POODLE attack became public. We more recently decided to finally disable SSL 3.0 entirely to completely eliminate the issue.