/ip firewall filter
add chain=input protocol=tcp psd=21,3s,3,1 action=add-src-to-address-list \
address-list="port scanners" address-list-timeout=2w comment="ip hacker to list" \
disabled=no

add chain=input protocol=tcp tcp-flags=fin,!syn,!rst,!psh,!ack,!urg \
action=add-src-to-address-list address-list="port scanners" \
address-list-timeout=2w comment="NMAP FIN Stealth scan"

add chain=input protocol=tcp tcp-flags=fin,syn \
action=add-src-to-address-list address-list="port scanners" \
address-list-timeout=2w comment="SYN/FIN scan"

add chain=input protocol=tcp tcp-flags=syn,rst \
action=add-src-to-address-list address-list="port scanners" \
address-list-timeout=2w comment="SYN/RST scan"

add chain=input protocol=tcp tcp-flags=fin,psh,urg,!syn,!rst,!ack \
action=add-src-to-address-list address-list="port scanners" \
address-list-timeout=2w comment="FIN/PSH/URG scan"

add chain=input protocol=tcp tcp-flags=fin,syn,rst,psh,ack,urg \
action=add-src-to-address-list address-list="port scanners" \
address-list-timeout=2w comment="ALL/ALL scan"

add chain=input protocol=tcp tcp-flags=!fin,!syn,!rst,!psh,!ack,!urg \
action=add-src-to-address-list address-list="port scanners" \
address-list-timeout=2w comment="NMAP NULL scan"

add chain=input src-address-list="port scanners" action=drop \
comment="dropping port scanners" disabled=no

SUMBER : http://wiki.mikrotik.com/wiki/Drop_port_scanners