Q: After the security update 2015-002 in OSX10.9.5, the system ask permission for an app called "Postgres" to accept incoming network connections. What is this and what to reply to the question ?

http://en.wikipedia.org/wiki/PostgreSQL

I did the same security update and did not get this request.  If you do not recognize I would not permit its use.

After reading the wikipedia article, I'd leave it turned off. It doesn't appear that doing so will cause problems for your computer.

You are welcome.

out of curiosity, did you have SL on your machine at one point? Did you get teh mac_kernel icon showing up in your computer tab after running the update?

A quick query about "mach_kernel"

Thanks Eric, found the answer both in another thread and in Apple's kbase on the issue right after posting this.

You are welcome.