Security risks with iframe

Hi Friends,

I had bookmarked this forum some time ago and totally forgot about it. In the meantime I had many questions arising time to time during projects and was only able to find answers through Google searches. Now I realize being the member of a community brings many advantages, so cutting it short, here is my question:

I am using an iframe on one of my websites. The iframe source is an external website and it has a secure part as well. My question is, when a user communicates through my website which is hosted on http, and it uses an external website which has some bits on https, What would you say about the security? Is there any security risk involved in this approach and is the communication safe?

Thank you very much for your time in advance,

cheers

swordfish