Opera, which has seen increasing popularity since the browser was made free, has recently been hit by a nasty glitch. Asking Opera users to upgrade to 9.02, versions 9.0 and 9.01 are vulnerable to a crash and potential other malicious action to a flaw in the way Opera handles certain long URLs. It could potentially lead to compromise:

The flaw means that vulnerable versions of the browsers will crash when visiting maliciously constructed web sites containing overly long (more than 256 bytes) URLs. Successful exploitation of this heap-based buffer overflow flaw creates a means for hackers to load malware onto the machines of visiting surfers.
It's being listed as “moderate”, and does not affect the newest version nor versions 8 and prior. If you are using 9.0 or 9.01, it's a good idea to upgrade. Whether you are using the Windows or Linux build, you are vulnerable.