See my answer here What did Blackberry do wrong?
I provide a link to the blog of a company that makes software to crack passwords. They include a single link to their software, but they also include links to other places.
The blog is relevant to the topic. I have no connection to the company. It is not a referrer link.
Is that link acceptable? Or is this bad practice that should be avoided?
That's fine. On the Stack Exchange network in general, promotion, even self-promotion, is not banned outright. It is considered acceptable to link to commercial sites if they are germane to the discussion. What is considered unacceptable is linking to your own site or product without disclosing that it's your own, or being present on the site exclusively to promote your own products.
From the FAQ:
May I promote products or websites I am affiliated with here?
Be careful, because the community frowns on overt self-promotion and tends to vote it down and flag it as spam. Post good, relevant answers, and if some (but not all) happen to be about your product or website, so be it. However, you must disclose your affiliation in your answers.
See also the FAQ on the main Meta on self-promotion and spam.
