MSN released version 7 of their Messenger yesterday.
In addition to some other new features, the new version also incorporates functions to prevent the spreading of malware.
The developers have taken some serious steps to prevent the sharing or spreading of .pif files. Any incoming or outgoing message with a ".pif" in it will be blocked completely.
Too bad that MSNM doesn't tell you that this is happening. Messages won't get delivered to the recipient, but neither the recipient nor sender will be notified that the message has been blocked. Not very user-friendly, IMHO.
In addition to filtering messages, MSN 7 also filters incoming file transfers. This filtration applies to files such as executables (with extensions such as .exe, .com, .scr etc) and other potentially dangerous types of file such as .vbs and .reg.
We've already seen IM-worms which spread in the form of a link to .scr files, so the measures that MSN developers have taken won't be 100% effective. But I think the complete blocking of .pif files is the most important innovation, as it's IM-worms spreading as .pif files which have been the most 'successful' to date.
Although some users may not like this kind of filtering, I think in the long run we're better off. IM-worms are becoming more and more common. Sooner or later users will have to learn to live with security measures designed to combat their spread.