The company believes that the new compromises are related to a series of earlier attacks that exploited a to steal Plesk administrator and customer passwords.

"I guess, hackers grabbed Plesk databases and then suspended their violent activity about 2-2.5 months ago in order to lull Plesk owners' vigilance," a member of the Parallels team . "Now we are observing new round of the exploit that is based on the grabbed Plesk databases."

However, some of the affected users believe that a new vulnerability is responsible for their servers being hacked because the new attacks occurred after they patched the old vulnerability and reset all Plesk passwords.

In addition, it's rumored that cybercriminals are selling a previously unknown vulnerability for Plesk Panel version 10.4 and earlier on underground forums.

"We are currently investigating this new reported vulnerability on Plesk 10.4 and earlier," the company said in a on Thursday. "At this time the claims are unsubstantiated and we are unable to confirm this vulnerability and cannot confirm that this vulnerability is limited to any specific operating system."