VPS, PLESK

My VPS has been compromised and the server is being used to send spam.

I need you to identify the script or weakness and remove or fix.

If you are bidding on this job, and I accept your bid, you need to start and finish the job today.

See latest headers below:
Return-Path:
Received: from [109.104.78.21] by usfamily.net (USFamily MTA
v5/:PG9ubGluZWJhbmtpbmdAYWxlcnQuY29tPjx0aGVwb21yb3lzQHVzZmFtaWx5Lm5ldD4-)
with SMTP id for
; Mon, 09 Jul 2012 14:41:30 -0500 (CDT)
(envelope-from onlinebanking@alert.com)
Received: (qmail 11345 invoked from network); 9 Jul 2012 20:14:49 +0100
Received: from unknown (HELO alert.com) (69.15.231.133) by
lvps109-104-78-21.vps.webfusion.co.uk with SMTP; 9 Jul 2012 20:14:49 +0100
Reply-To:
From: onlinebanking
Subject: Security Issue
Date: Mon, 9 Jul 2012 15:12:46 -0400
Message-ID:
MIME-Version: 1.0
Content-Type: text/html; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable