Google Adsense in Belgium

is there anyone here from Belgium who makes decent money with Adsense (at least 500 per month). I wanna know if it's better to let taxes know about this income or not. Any other people experienced with Adsense + taxes are welcome too.

Is it ok to drive +200km/h on the highway? Yes as long as they don't catch you!

But i'm asking how big the chance is if they'll catch me and if there is a difference if i drive 150 km/h or 250 km/h

I'm from Belgium, the chances are very small/almost non-existant that they will catch you. Once you get to 1.000 euro/month you should register a business though. So it's only if this your only "extra" income, else I would definately get a business which is pretty cheap and fast to set up, you just need to get a VAT-number.
The main problem is that once it's an official income you'll lose 35-45% to taxes.