You can't. New users are prohibited from posting links except to specific trusted sites.
Means only newbies can't post external links to other untrusted websites? I have often seen newbies/junior members posting links of malicious websites/software links but that wasn't prohibited. I used to report those threads and they used to get deleted then.
I have seen the same. Especially spam with referrals, etc. I know lower level members have been able to do it in some cases.
Maybe Foxpup can explain more to us how it can happen, without all the personal jabs.