Security firm Symantec has used the first anniversary of the Conficker/Downadup 'activation' date to warn users that the botnet could still "wreak havoc".
Security professionals across the globe were braced for trouble on 1 April 2009, after news emerged that PCs infected with the Conficker.C worm would connect to a control server on that date, as a prelude to a possible attack.
In the end no such attack materialised, but 6.5 million systems are still infected with the .A and .B variants, and a few hundred thousand with the .C variant, and the botnet still represents a significant threat, according to Symantec.
"With millions of infections in the wild, Downadup should not simply be laughed off," said a Symantec Security Response spokesperson in a video posting on YouTube.
"An attack from a botnet of this size could still wreak havoc, and precautions should be in place in case it does."
Symantec advised firms to keep software, operating systems and security systems patched and up to date, and to download the W32.Downadup Removal Tool if they notice any infections.
Microsoft comes up with a new way to foist its unloved and little used Edge web browser on people
Facebook suspends Cambridge Analytica following weekend claims that it illegally harvested information from 50 million users
Insider claims Cambridge Analytica used academic app to filch Facebook data of 50 million users
Is the Samsung Galaxy S9+ worth its high price?