The DigiNotar Certificate Authority got hacked and a lot of SSL certificates were issued for common sites (google, microsoft, amazon, etc), allowing the hackers to pretend to be these sites without the user being able to tell there's a problem. It took DigiNotar a long while to find they'd been hacked, and even longer to admit that they didn't really know how many (and which) certificates had been issued.

The end result is that DigiNotar have been blacklisted by all the browsers (which is what this update will add for the Maemo browser), preventing any certificates signed by them from being accepted. The company has since (inevitably) gone out of business.

The suspicion is that Iranian hackers (possibly government sponsored) were behind this - there's certainly evidence of a huge increase in related lookups from Iran shortly after this hack.

You can see a preliminary post-mortem on this attack here.