PartitionCleaner

PartitionCleaner is an application capable of creating a temporary directory on any partition to fill it with large files of random data.

Fill free disk space with random data

Its purpose is to occupy the free disk space to prevent specialized software from recovering important files without your permission. It can also be used for testing defrag applications.
The main window shows all options in plain sight, along with instructions. All you have to do is select one or more drives whose files you want to protect and pick the overwriting method.

Select the partitions and overwriting method

You can choose from random with one pass (fast but medium security), random and xor of random with two passes (slower, but higher security), 1010.. with 1 mass (fast but medium security) and 1010.. and 0101.. with two passes (slower, but higher security).
Additionally, you can instruct the tool to delete the temporary folder when the task is done, as well as to launch the Windows format tool to format the selected partitions before creating the files (which erases all your data).

Set the block size, file size, and number of files

The task can be stopped if you change your mind. In addition, it's possible to launch the Windows Disk Management utility on the spot if you want to re-arrange your partitions.
As far as extended settings are concerned, you can modify the default block size (kilobytes) and file size (megabytes), as well as limit the file creation number to any number of files.

Conclusion

We haven't come across any compatibility issues with the latest Windows edition in our tests, although PartitionCleaner hasn't received updates for a considerable amount of time. It uses a significant amount of system resources while creating the dummy files. Thanks to its straightforward options, it can be easily used.