Mac and Windows users are being advised to upgrade to the latest version of QuickTime.

Secunia warns that vulnerabilities within earlier versions of QuickTime exist. These can be exploited by malicious people to cause a DoS (Denial of Service) attack and potentially to compromise a user's system.

These vulnerabilities mean hackers can build video clips containing code that can be made to execute just by running the movie. Hackers can also build movies that will crash applications that use QuickTime.

A fourth flaw affects PICT data when using QuickTime to look at still images. Again this can allow arbitrary code to run.

Vulnerabilities have been reported in the following versions of QuickTime: QuickTime version 6.5.2 and 7.0.1 for Mac OS X; QuickTime versions 7.x prior to 7.0.3 for Windows.

Users should update to QuickTime 7.0.3, the security analysts said.