Add to that the Nimda worm, starting about September 18, 2001, and probes to tcp:80 have become so common as to have become background noise: sure, the probes are potentially malicious to unpatched/poorly maintained Window$ boxes, but the relentless drizzle of probes itself has become something too easily ignored...
I've often wondered if some of these are actually deliberate probes, rather than the spontaneous emissions of compromised Window$ boxes.
Here's a pretty typical example, this one's from a university down in Mexico:
Unusual System Events
=-=-=-=-=-=-=-=-=-=-=
Feb 19 05:47:22 greatwall snort: [1:0:0] Potential CodeRed/Nimda probe {TCP}
148.204.4.1:3681 -> 12.82.133.142:80
Feb 19 05:47:31 greatwall last message repeated 2 times
Feb 19 05:47:22 greatwall kernel: Packet log: input DENY ppp0 PROTO=6
148.204.4.1:3681 12.82.133.142:80
L=48 S=0x00 I=56890 F=0x4000 T=111 SYN (#64)
Feb 19 05:47:26 greatwall kernel: Packet log: input DENY ppp0 PROTO=6
148.204.4.1:3681 12.82.133.142:80
L=48 S=0x00 I=56983 F=0x4000 T=111 SYN (#64)
Feb 19 05:47:31 greatwall kernel: Packet log: input DENY ppp0 PROTO=6
148.204.4.1:3681 12.82.133.142:80
L=48 S=0x00 I=57151 F=0x4000 T=111 SYN (#64)
Tue Feb 19 05:47:22 2002 148.204.4.1 [18 hops]: Windows 2000 (9)
+ 148.204.4.1:3681 -> 12.82.133.142:80
Tue Feb 19 05:47:26 2002 148.204.4.1 [18 hops]: Windows 2000 (9)
+ 148.204.4.1:3681 -> 12.82.133.142:80
Tue Feb 19 05:47:31 2002 148.204.4.1 [18 hops]: Windows 2000 (9)
+ 148.204.4.1:3681 -> 12.82.133.142:80
BW whois 2.9 by Bill Weinman (http://whois.bw.org/)
© 1999-2001 William E. Weinman
NIC-Mexico (NETBLK-REDMEX-BNETS)REDMEX-BNETS
148.203.0.0 - 148.250.255.255
Instituto Politecnico Nacional (NET-IPN-MX) IPN-MX
148.204.0.0 - 148.204.255.255
Instituto Politecnico Nacional (NET-IPN-MX)
Juan de Dios Batiz s/n Col. La Escalera
Mexico, DF 07738
MX
Netname: IPN-MX
Netblock: 148.204.0.0 - 148.204.255.255
Coordinator:
DCyC, NIC - IPN (NID1-ARIN) nic@conectividad.ipn.mx
+ 52 55 57296000 ext 51404
Domain System inverse mapping provided by:
APOLLO.TELECOM.IPN.MX148.204.103.2
GODEL.ESFM.IPN.MX148.204.102.3
"Instituto Politécnico Nacional
Miguel Othón Mendizábal s/n Col. Residencial la
Escalera 07738
Tel. 57296000,
México, D.F., México"