Partially the spread like that of forest fire can be accounted for different paths how Vundo sneaks into systems. That's why common antivirus protection often fails to spot the threat. Among popular Windows-based PC vulnerabilities, the following are most widely exploited by Trojan Vundo and its clones:

Downloads of shareware programs from unsafe websites (like P2P networks – torrent, limewire, emule, etc). Malicious code is added to executable installation files of popular products – i.e. antivirus software, parental controls, etc. – and distributed via websites visited by millions of people daily. It is important to know that a contaminated executable of a legit program is unlikely to be spotted as dangerous. Whenever you start executing the file, that is, double-click it, infection takes place immediately. Parts of the Vundo virus are places in different folders and related to the Windows registry with autorun keys;

There's a documented vulnerability in Java installation. Though the problem has been fixed by an update released by Java developers, there are many computers with outdated Java;

Windows Operating System itself is vulnerable to Vundo which is able to exploit security breeches. Although Microsoft released patches, due to different reasons a lot of PC users haven't applied them yet, leaving their computers at risk of infestation;

The use of all kinds of illegal software patches poses a great risk; code of Trojan Vundo is often embedded into cracking programs.

The conclusion is simple; to minimize the chances of getting infected with Vundo virus, it is crucial to have all software programs updated; same applies to Windows. Automatic Updates offer an easy way to stay protected. Also, download any programs from manufacturer websites only, or use trusted, reputable resources. These are all simple steps, yet they significantly decrease the risk of devastating a computer with a trojan Vundo.