ark-lock.dat definition, relationships, removal:

The ark-lock.dat file is an essential part of a particular parasite and therefore is responsible for the pest's malicious activity. Exact purposes of ark-lock.dat depend on the related parasite's type and carried payload. Some threats can use ark-lock.dat to serve annoying pop-up advertisements or store certain configuration settings, while others need it to corrupt files, steal user confidential information or run a spreading routine. In any case, DO NOT open this file!
The ark-lock.dat file is installed and used by AOL parasite ARCS-FAC.
Sometimes a presence of ark-lock.dat does not indicate that your computer is infected. It can be an essential system file or a file installed by harmless legitimate software and therefore may not pose any threat to your privacy and the system. Although such cases are quite rare, you should thoroughly examine ark-lock.dat before completely deleting or leaving it in the system.