All "ICMP echo request" (or PING) packets to our users will be filtered since a virus "Welchia" is scanning for active machines to infect by sending an "ICMP echo request" (or PING), resulting in increased ICMP traffic and network latency. For detail of the virus, please check:

http://www.hkcert.org/valert/vinfo/w32.welchia.worm.html

Sorry for any inconvenience caused.