Downadup or sometimes known as Confick or Conficker, is said to be the most infectious worm to date.
If you remember, Microsoft issued an alert sometime in October of last year and issued an emergency security patch for Internet Explorer. The patch number is KB958644. If you have this, then you should be save.
However, even if your system has been infected, it may be possible to totally remove it by downloading and installing the free Malicious Software Removal Tool (MSRT).
What makes Downadup all the more dangerous is that it has a list of passwords which it will try on infected systems to gain access to administrative rights.
One of the major points to look out for if your system has been hijacked is to see if you could log in to various accounts or websites because your password has been changed.
If that is the case, download the malicious software removal utility right now.