Those are in-universe classification levels. It says low-level personnel are not allowed to access this file, only Level 4 and O5, the latter being the top tier Foundation ruling council. So that one can't really be decoded without a bit of SCP-specific knowledge.

This part is talking about who is allowed to view the materials. Level 4 and O5 are the top people of the foundation and the information is only allowed to be seen by them.

Probably that the data contained therein is authorized for foundation members at O5 and O4 level

http://www.scpwiki.com/security-clearance-levels

O5: http://www.scpwiki.com/o5-command-dossier

Information must only be shared with those of level 4 clearance or higher.

Edit: Oh wow, a lot of people replied between my last page refresh.

Information about this SCP is not to be given to anyone with a clearance level below level 4. (Including the O5's)

Can't edit: AND* the O5's.

Access to information restricted to Level 4 clearance and O5 council only.