As we've reported before, there's strong evidence that forces with widespread access to Iran's internet infrastructure have been engaged in large-scale surveillance of https traffic in July and August, certainly of Google traffic, and perhaps many more websites, including Facebook and Yahoo!
If you used the Internet in Iran during this period you should, at the very least, change your passwords, and log out, then log back into, any services you use.
A fuller explanation of what happened, and what to do about, written in Farsi, is available from Google's Persian Blog. "DigicomV" on YouTube has also posted some Farsi-language videos explaining the attack.
Thanks to Katrin at MobileActive for these links.