Hacker group LulzSecReborn has targeted CSS Corp and Military Singles' sites, publishing data reportedly taken in the cyber raid online.
The hackers claim to have obtained the email details for all staff at IT services firm CSS Corp, and have published some details online.
Prior to the attack on 25 March, LulzSecReborn published what it claims are the names, usernames, passwords, and emails of 170,937 accounts on MilitarySingles.com.
The group has since suggested it still has access to the two sites' networks and could delete CSS's information at will.
and admins from csscorp I know that you are smarter then the others please don't search for proof we will delete your whole database... #CSS— LulzSec Reborn (@lulzboatR) March 26, 2012
Neither CSS Corp nor Military Singles had responded to V3's requests for comment at the time of publication.
Meanwhile, LulzSecReborn said it is not affiliated to the original LulzSec group and has no knowledge regarding the authenticity of LulzSec's rumoured April Fools' Day return.
"We are not the old LulzSec. The idea is to continue what some have started and never managed to finish. At the same time we want to avenge the ones that were arrested," Softpedia quoted one group member as saying.
Rumours the original group would return arose after a video appeared on YouTube on 17 March promising LulzSec would launch 'Operation Lulz Day' on 1 April.
Housing little more than images of LulzSec's mascot with the group's 'lulzboat theme song' playing in the background, the video gave no hint what would actually happen on 'Lulz Day'.
The original LulzSec group ended its hacking spree nine months ago, reportedly because its members feared arrest. During its active period the group had mounted successful cyber attacks on several high-profile targets including The Sun, Sony and the FBI.
The new group has, however, been dismissed as "inconsequential" by some security researchers.
Sean Sullivan, security advisor at F-Secure told V3: "I think such copycat groups are likely to be more common, but they’ll be inconsequential."
While other hackers may look to gain notoriety from being associated with the LulzSec brand, there was little sign that they would be as effective as the original group, he added.
"There are very few signs that those acting in this new LulzSec campaign have any good idea how re-launch that brand in a way that would be on par with what Jake Davis (aka Topiary) helped build," said Sullivan.
"It’ll take more than a Twitter account and some database dumps for this new LulzSec group to be taken seriously."