Troj/Boa-A is a keylogging Trojan. The Trojan monitors keypresses and other system activity and periodically sends an email to the attacker containing a log of the actions monitored on the victim's machine.
When Troj/Boa-A is first executed a copy will be created in the System folder with the filename msnet.exe and the following two registry files will be created so that the Trojan is run when Windows starts up:
HKLM\Software\Microsoft\Windows\CurrentVersion\Run\msnet
HKLM\Software\Microsoft\Windows\CurrentVersion\RunServices\msnet
Troj/Boa-A also fills up the user's hard disk with JPG files in the Windows system folder with the filenames file000.jpg, file001.jpg, file002.jpg, etc. These JPG files contain snapshots of parts of the user's Desktop and are intended to be emailed to the attacker along with the other logs.