Opera has issued a security patch to protect users against flaws in some versions of its browser running on Linux or Unix, and in Macromedia's Flash Player. 

Opera 8.51 addresses flaws that could allow a hacker to remotely take control of a user's system, according to a statement from the browser developer.

The company has made a change to the wrapper script so that shell commands that let users enter text that is fed to the script will no longer be executed.

According to an advisory from security researcher firm Secunia, a vulnerability was detected in versions of Opera 7 and Opera 8 running on Linux, FreeBSD or Solaris. 

The flaw allowed an attacker to remotely execute arbitrary shell commands by tricking the user into clicking on a link to a malicious website.

The vulnerability is a variant of a problem that affected the Firefox browser in September, about which Secunia gave its highest rating of extremely critical. 

Last June, Opera issued a patch, the 8.01 update, to address several security flaws including some that could be exploited by phishers.