perflib_perfdata_***.dat (Performance library, Performance Data)
Perflib_Perfdataxxx.dat Files Accumulate Under %SystemRoot%\System32
These files are generated by processes in the normal course of operation; however, files are orphaned when you do not shut down a computer properly, such as by pressing the power button on a computer...
Perflib_perfdata_***.dat files are sometimes created by Windows System Monitor
and other disk monitoring software such as Diskeeper. When you shutdown normally, the file(s) should be deleted but as Microsoft advises, if you have an abormal shutdown, they can become orphaned and accumulate on your computer. Under some circumstances it has been reported that these files can become orphaned during normal operation. See What are the %SystemRoot%\System32\Perflib_Perfdataxxx.dat files?
They may be found in various locations:
C:\Documents and Settings\username\Local Settings\Temp\Perflib_Perfdataxxx.dat
These files can safely be ignored. However, you can use ATF Cleaner
to clean up the files in the temporary directories except for the most current one which is probably locked if its in use. When a file is locked that means it is protected by the operating system and explains why it shows as "Skipped" or "Access Denied" in certain log scan reports.