Legit users don't need to worry unless the code to generate a legit console ID is cracked. Look at the size of the console ID -- it's 25 digits long. That means there are 10 septillion possibilities. Even for a computer, it would take a very long time to brute force through every possible ID, or even just randomly stumble upon a valid one.
On top of that, you'd have to verify each ID against PSN. It wouldn't take Sony long to implement a strategy to counter that, assuming they don't already have such a strategy in place.
For example, if I was to write such a system (no Sony, I'm not asking for a job), I'd put a delay of 5 seconds before the system would respond to a login request. For a regular user, 5 seconds is hardly noticeable, however for someone brute forcing all possible IDs we're talking about 1,500,000,000,000,000,000 years. Even with every computer in the world working on that, it's going to take forever.
As secure as that probably is, I'd still take it a step further. Let's double the delay after each request. Let's say the first request gets a delay of 5 seconds. The second is doubled, making it 10 seconds. Then 20, 40, 80, 160, etc. At this rate, it takes over 5 minutes to check a measly 6 IDs. Nearly an hour and a half for 10 IDs.
And for the record, if the console IDs are truly random, then any given number is just as unlikely to be legit as the next. That means searching through all possible numbers in a random order does not make it any faster than just going 1 up each time.
I hope that helps put things in perspective for people.
And if you're looking to steal someone else's ID, please don't. Not only is it morally wrong, but you're now crossing a line and possibly facing serious consequences depending on your country's laws. At best, you screw over someone who paid an honest buck for his console.