Non-Compete clause in Employment Agreement

I am currently employed with a leading consumer internet firm & my appointment letter has a clause stating that I can't work in a competition company for 12 months. Now, I am considering an employment offer from a competition firm where many of my office colleagues have joined in past year. While my existing company didn't take any legal action against them but considering my position & access to information, I am concerned about legality of the clause. Can you please advice if such a non-compete clause is practically enforceable in court and if yes, what is the worst outcome for me if I do switch jobs?