_default.pif file is a dangerous graphics file, which belongs to Autosky worm that is also known as W32.Autosky. Leaving this worm on computer can easily initiate problems that are related to your security and privacy, so be sure you remove this dangerous program from the system as soon as you can. Otherwise, it may be used for a remote connection to your affected computer or other activities that are typically initiated for stealing people's logins, passwords and other sensitive information.
As soon as _default.pif is created, it is used for degrading system's performance. However, sometimes a presence of this file does not indicate that computer is infected. It can be an essential system file or a file installed by harmless legitimate software. Although such cases are quite rare, you should thoroughly examine _default.pif before completely deleting it or leaving it in the system. For that you can use RegCure Pro.