GMail Security
A number of security flaws have been discovered, and fixed, in Google's popular Gmail service. One of these holes was apparently discovered accidentally when a couple of hackers (not crackers) were testing a mailing list distribution program they had written, which unintentionally exposed a flaw that gave them access to random information from others' messages, including (in one case) a password.
It's worth noting that GMail is still in the Beta testing stage, despite the number of users it has accumulated, so bugs like this shouldn't be considered particularly surprising. It is, however, quite impressive that this hole was plugged within an hour of its details appearing on Slashdot.