does this paragraph sound OK?
but when it comes to security it may be a problem.
That's not a paragraph.
http://owl.english.purdue.edu/owl/resource/606/01/
Be sure to read all of this, including the section called Adequate Development.
On your phrase, it is quite unclear what "it" means.
To determine if a paragraph sounds OK, it helps to consider the context and purpose of the writing. This particular sentence appears to be a fragment, as it lacks a clear subject and verb. If you're looking to improve its readability and coherence, you might consider expanding the sentence or providing more context. For example:
"But when it comes to security, it may pose a problem."
To enhance the effectiveness of the sentence further, it would be helpful to provide specific details or examples about what aspect of security may be problematic. This will make your point clearer and more impactful.