All Plesk versions from 7.x to 10.3.1 are affected by a security flaw. Plesk 10.4.x and newer, already include a security patch and are not affected. This security flaw enables the attacker to gain root or administrator access through an SQL injection. The Parallels Knowledgebase offers more information on this vulnerability.
For example, list the files in this location and check for unfamiliar results:
The file "scatterly" is an unfamiliar file and which is run regularly by the server. Use the cat command to find more information about the cron jobs
If your system has not been compromised, do one of the two following:
If your server has been comprised, you cannot update Plesk or perform a patch. The root or administrator accounts may already be accessible to attackers. Backup your data and re-image the server to an OS that includes a newer version of Plesk, or one that does not include Plesk. Choose new passwords for your server.