Yep, don't say anything on message boards that you aren't able to answer for in the future.
If you got any unsavory business or actions going on, keep it face to face and avoid writing anything down.
These days, if the cops have reason to suspect you for any crime, the first thing they do is come to your house and confiscate your PC hard drives. Down here in Oz, the cops don't even need a warrant to come into your home. All they need is reasonable suspicion, which is discretionary. I don't agree with those invasive laws, but there they are.
Last year, my neighbor was growing some baby marijuana plants out on his balcony. Not for using or selling, just as kind of a joke. Anyways, a girl who didn't like him ratted him out to the cops. The only problem was she gave the wrong address... She gave MY address. It was 10:00AM the next day, I was still asleep. Next thing I know I have two big cops standing over my bed nudging me awake and a flashlight in my eyes, telling me to wake up. They took my computer and I sat in the back of a squad car for 3 hours while they were busy figuring out that I wasn't who they were looking for. After the dust settled, my neighbor got expelled from uni and put in jail for nine days (He had incriminating text messages and numbers on his cell phone).
So yeah, no written or saved incriminating evidence is safe. Imagine if I'd had files on my computer about how to grow weed and numbers of some dealers, etc.
cheers