Rootkit.Duqu.A is digitally signed with a stolen digital certificate that has been revoked in the meantime. The rootkit runs on the computer for 36 days and collects any kind of information entered via the keyboard. After the “surveillance” period ends, the rootkit gracefully removes itself from the system. Rootkit removal can be challenging even for some antivirus solutions, so manual removal is not recommended. You only have to download and run it on the system, then reboot the PC if infection is found.
Source: https://thehackernews.com/2011/10/stuxnets-son-duqu-removal-tool-released.html