Ubuntu Security :: Decide If A New Program Have Installed Is Malware Or Not?

In Ubuntu 10.04 LTS, I have downloaded and installed texlive (2011). They have issued the following warnings:

1. "To the best of our knowledge, the core TEX programs themselves are (and always have been) extremely robust. However, the contributed programs in TEX Live may not reach the same level, despite everyone�s best efforts. As always, you should be careful when running programs on untrusted input; for maximum safety, use a new subdirectory."

What does this exactly mean? The installed program has already created own directories and subdirectories (e.g. /usr/local/texlive/2011/bin/i386-linux). Am I supposed to create a new subdirectory in home to write files and run latex program? Exactly how do I know that the downloaded and installed program is not malicious?

2. "Finally, TEX (and its companion programs) are able to write files when processing documents, a feature that can also be abused in a wide variety of ways. Again, processing unknown documents in a new subdirectory is the safest bet."

what is implied by "a feature that can also be abused in a wide variety of ways".