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For those whymers.

Yahoo Messenger users who haven't updated recently may be open to attacks by malicious users through a buffer overflow vulnerability. According to a report by Secunia Security, Messenger versions prior to 5.6.0.1358 are affected. Yahoo fixed the problem in version 5.6.0.1358. To check your version, start Yahoo Messenger, click on the help menu item and then click on About Yahoo Messenger. The version number should be right there ( Figure 2 ).
If you have an older version, you need to uninstall it before updating, since the new version does not remove or overwrite the older one.

Source: http://www.pcmag.com/article2/0,4149,...153,00.asp