This indicates an attempt against an integer overflow vulnerability in Opera.
The vulnerability is caused by a buffer overflow error when processing malformed HTTP "Content-Length:" headers. It can be exploited by remote attackers to crash an affected browser or execute arbitrary code by tricking a user into visiting a web page hosted on a malicious web server.
Opera Software Opera Web Browser 10.50
Opera Software Opera Web Browser 10.10
Opera Software Opera Web Browser 10.1
Opera Software Opera Web Browser 10.01
Opera Software Opera Web Browser 10
System Compromise: Remote attackers can gain control of vulnerable systems.
Upgrade to the latest version, available from the website.