thecoalman - 8:12 am on Mar 10, 2011 (gmt 0)
...and that it is frequently compromised.
That can be said about phpBB2 but that is not the case with phpBB3. Before it's release it went though a paid security audit with no major vulnerabilities found. It's track record since it's release in late '07 is outstanding.
As far as SEO goes out of the box it's not that great but there is lot of great modifications available.