Most of the downloading sites I have come across announce that the patch may not be virus or trojan free.
It is important that you be extremely sure about the download source and its reputation before going ahead with the wow patch 2.4.3 download and install because the scammers may exploit this demand to spread their nefarious designs.
Gamers are juicy targets.
I will be scanning the net for good sources and post it here. Keep checking back for updates.