This is not true, if you check the virus total report, there are:
49 antiviruses like ( AVG, Kaspersky, Bitdefender, Microsoft and other top antiviruses ) that say it's clean
vs
5 antiviruses i have never heard of ( Rising, Antiy-AVL, Ikarus, Jiangmin, AegisLab ) that say it's virused
you can check the report yourselves here: https://www.virustotal.com/de/file/6f781ac71a826179156deded922caf62fa337c0489c002c9a14a15b18bd67a04/analysis/1453405221/
Adding to it, the known fact, that there are patched files like every l2 server uses, you will get the answer why a few no-name antiviruses see them as a virus.
Check the virus report above, there patch is not full of viruses.
Thank you.