Download Opera 7.22, a security problem was found. It is unlikely to be exploited, but possible. Also, if you have not yet upgraded to Sun Java 1.4.2_01, then you should download Opera 7.22 with Java (two birds, one stone). There was a Java security problem which was unrelated to Opera. You need to update Java regardless of whether you use Opera or Mozilla/Firebird or IE.
Of course, if you use IE you need to update a lot more security patches…. just today there was another big one. Read about the latest security holes in Internet Explorer.