Flashback.K was followed by Sabpab, a different piece of malware that exploited the same Java vulnerability even though Apple had by then released a Java update that plugged the security hole. (Incidentally, Symantec has reported that the number of computers infected with Flashback.K had fallen to around 140,000 by Monday April 16, compared with over 600,000 at its peak.)
Now security vendor Kaspersky is saying that an earlier - though highly targeted - version of Sabpab has been in circulation since February. That variant exploits a Microsoft Word 2004 and 2008 vulnerability that was patched by Microsoft in 2009.
While keeping your system current with regard to security-related updates doesn't guarantee you won't be affected by malware (as Flashback.K demonstrated), it does close a large proportion of the doors that the Bad Guys know about. Indeed, a high percentage of malware infections on Windows machines are said to involve old vulnerabilities that should have been patched.