For DS owners beginning to feel left out by
that PSP Trojan circulating online right now, a hacker by
the name of DarkFader has managed to bring that brick-making
goodness to Nintendo's previously protected portable as well.
So unless you want a $130 brick on your hands, try to avoid anything by the likes of r0mloader (supposedly named that way to combat piracy) or taihen (which was said to be a hentai-filled ROM). This little Trojan homebrew will reportedly wreck your DS (unless you preemptively ran FlashMe) and "affect your GBAMP firmware and/or your SuperCard Firmware," too.
Remember, kiddies: handheld firmware is a terrible thing to waste, so play safe, and homebrew with your head. Here's a similar link from Engadget.
[Thanks, anonymous, Covarr, JonathanEx, and Nico]