Plesk Panel is one of the most widely used administration panels for Web hosting servers. It provides users with a graphical Web-based interface that allows them to easily perform server administration and website management tasks.

Since the middle of June, thousands of websites have been infected with malicious code that to make attacks more persistent. The hackers behind the wave of compromises are using a new version of the Black Hole exploit toolkit.

The affected websites were built using a variety of technologies, including HTML, PHP and ASP.NET and were hosted on different types of Web servers, including Microsoft's IIS, Apache and Litespeed, independent security researcher Denis Sinegubko said in a on June 22. The only common element among them is that they are all hosted on servers that use Plesk as a management panel.

"It's a very massive attack and it is limited to Plesk servers," Sinegubko said Friday via email. "So it definitely has to do with some Plesk security issues."

The attacks are ongoing and reports from Web hosting server administrators whose systems were affected in Parallels' support forums.