This indicates an attack attempt to exploit an Information Disclosure vulnerability in Magmi database client.
The vulnerability is caused by an input validation error in the "download.php" while processing an HTTP request. Remote attackers may be able to exploit this to gain unauthorized access to sensitive information via a crafted request.
Magmi version 0.7.21 and the prior
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Currently we are unaware of any vendor supplied patch for this issue