Security Vulnerability in WPMU Membership?

Hello - on our site we use Membership plugin to have people pay for access to premium content, such as videos, audio files, etc.

Someone emailed our support line saying that they wanted to give us a heads up to a potential security vulnerability. He claimed that by using his premium account login information, he would be able to use an "iFrame" and embed premium content on other websites (circumventing the need for payment). Is this true? If so, is there something we can do to stop this??

Thanks and regards,

AD