It seems that in the very popular AV suite Symantec Anti Virus, there exists a vulnerability in the way theis programs handle the scanning of RAR files. Since RARs are often used as containers for executables containing viruses, they are often automatically scanned on systems with these suites. The problem could result in a heap overflow that results in potential arbitrary code execution, resulting in a compromised system. A cleverly designed RAR is all it takes, and it could even happen automatically - the scan of the file itself is enough. Read more information here. It's considered more important than usual as often with the coupled e-mail protection, e-mails containing RARs are scanned automatically.