File in question has some serious security issues given the subfolder amltd which -also- contains a shell script.
Here's the short and bad, so to speak. It's permanent given how long the files have been on there. At the time they were uploaded, they had been scanned and did not match any current filters in the system.
At the time.
Scipt.php had been accessed today: Access: 2011-04-29 09:23:36.000000000 -0400, and it was due for rescan, and there was now a filter for the c99 series of webshells. It suspended for it. Here's the bad part - that file's modify date. Modify: 2007-12-26 01:31:35.000000000 -0500 - approximately 25-30 days after the accounts original creation. No one used it for 3-4 years which is why it went undetected until now.
Worse, the script I located in the amltd folder, specifically amltd/images/mshell.php. This one was -also- accessed today, and last modified back on september 26th 2009. Same problem - scanned and found to be clean at the time, but then accessed later and re-scanned and found to be a major problem.
The amltd folder appears to have contained a php file uploader of some form, which is quite possibly how these malicious scripts got onto the account. Sadly, there's nothing that can be done - you're responsible for the contents of the account, and these have been here for quite some time before someone tried to run them.