The invention relates to modified nanoparticles based on pyrogenic silica which are produced by treating pyrogenic silica with compounds of the general formula I Me(OR.sup.1).sub.4, and/or of the general formula II Me(OCOR.sup.1).sub.4, wherein R.sup.1 means an alkyl, aryl and/or aralkyl residue and Me means zirconium and/or titanium and to coating compositions containing the modified nanoparticles.