It's now trawling the internet, similarly to Google, to build up its database.

The reason this is bad is as follows:

Turnitin is a for-profit organisation and generates money from indexing your stuff, with no permission given by yourself, and at no possible benefit to yourself. It doesn't reimburse you, it doesn't cite you, it just presents your work as being [...]]]> If you've been to university recently you'll be familiar with Turnitin. It's a service that supposedly detects plagiarism in students' submissions. Students submit their paper to Turnitin, and Turnitin generates a report telling you it's x% plagiarised and contains sentences, paragraphs, or even chapters that look suspiciously similar to other papers in its database. It's also woefully stupid; when I did my Master's thesis (on ragdoll physics), Turnitin decided I'd 2% plagiarised from some biochemistry papers, and completely failed to detect any similiarity with other papers on ragdoll physics.

It's now trawling the internet, similarly to Google, to build up its database.

The reason this is bad is as follows:

Turnitin is a for-profit organisation and generates money from indexing your stuff, with no permission given by yourself, and at no possible benefit to yourself. It doesn't reimburse you, it doesn't cite you, it just presents your work as being something it has an inalienable right to use for whatever it wishes. Whilst it is supposedly against plagiarism, it has no qualms violating your intellectual property and then making money off it.

Here's how you can block it:

robots.txt:

User-agent: TurnitinBot
Disallow: /

.htaccess:

RewriteCond %{HTTP_USER_AGENT} TurnitinBot [NC]
RewriteRule .* - [F]