Anyone who takes no precautions can expect to be hacked within hours.
Here is a summary of the break-in attempts on my home network since Jan 2, as blocked by the border router. Service names where known, port numbers where not known.
Code:
4499 microsoft-ds 2 rsh-spx
1448 ms-sql-s 2 radan-http
1409 49756 2 h323hostcall
733 telnet 2 cslistener
287 8909 2 81
195 epmap 2 27238
160 ms-wbt-server 2 21168
144 mysql 1 zenginkyo-2
74 ident 1 websm
42 9415 1 socks
39 http-alt 1 redstorm-diag
25 netbios-ssn 1 pcanywheredata
21 rfb 1 netiq
16 radmin-port 1 imap
14 https 1 iax
11 pop3 1 dsc
10 ndl-aas 1 distinct
9 6666 1 cisco-sccp
5 ncube-lm 1 cadlock2
3 codasrv-se 1 9944
3 65500 1 880
3 5998 1 8090
2 ssc-agent 1 37037
That is not counting the permitted services that were dropped by iptables rules at the server.