It seems that it is the (unofficial) browser fixing week this week, what with Microsoft, Mozilla and now bit-player Opera all having problems with 'critical' and (in Opera's case) 'extremely severe' security flaws.
Opera 9.63, released for download earlier this week, is only applicable to Windows PCs and is described as a 'recommended security upgrade'.
One problem fixed by the Opera update potentially allowed an attacker to take remote control of a computer, while another critical flaw meant that HTML could cause unexpected changes and trigger a crash.
The fix also dealt with a number of other issues from those rated 'highly severe' through to those without a severity rating.
Basically, if you use Opera, update it as soon as you can!
For more on these latest security issues with Opera check out the release notes for the update.