Symantec has warned of a fourth, unpatched zero-day vulnerability in Microsoft Word 2000.

A zero-day vulnerability refers to a security hole for which exploits are aleady available when it was discovered and the latest one, listed as "extremely critical", affects most versions of Windows running Word, says Symantec.
The attack comes via an infected Word document which, when opened, installs Trojan.Mdropper.W along with other files that enable hackers to control the infected computer.