strange behavior on Cisco 2801

[Marcin]

Hi!

im running Cisco IOS software on 2801 router (C2801-ADVIPSERVICESK9-M),
Version 12.4(3e), RELEASE SOFTWARE (fc2). I have few problems and i have
seen strange behavior: after few hours there was no responding from router,
no nat etc. After restart everything was ok for 10-12 hours.

I have ONLY one user name to permit logon via ssh to router: marcin and
not dictionary password (14 symbols)

I logon 2 hours ago and i use command "who". I was very surprised, because
i saw something in 1 minute 2 different usernames and NO USERNAME on vty
194.

i looks like that:

router#who
Line User Host(s) Idle Location
vty 194 idle 00:00:01 nt.math.nknu.edu.tw
* vty 195 marcin idle 00:00:00 210-az4-2.acn.waw.pl

Interface User Mode Idle Peer Address

router#who
Line User Host(s) Idle Location
vty 194 aivankovic idle 00:00:04 nt.math.nknu.edu.tw
* vty 195 marcin idle 00:00:00 210-az4-2.acn.waw.pl

Interface User Mode Idle Peer Address

router#who
Line User Host(s) Idle Location
vty 194 idle 00:00:01 nt.math.nknu.edu.tw
* vty 195 marcin idle 00:00:00 210-az4-2.acn.waw.pl

Interface User Mode Idle Peer Address

router#who
Line User Host(s) Idle Location
vty 194 aivankovic idle 00:00:04 nt.math.nknu.edu.tw
* vty 195 marcin idle 00:00:00 210-az4-2.acn.waw.pl

router#who
Line User Host(s) Idle Location
vty 194 idle 00:00:01
nt.math.nknu.edu.tw
* vty 195 marcin idle 00:00:00 210-az4-2.acn.waw.pl


router#sh users
Line User Host(s) Idle Location
vty 194 akrizan idle 00:00:40 nt.math.nknu.edu.tw
* vty 195 marcin idle 00:00:00 210-az4-2.acn.waw.pl

What is going on? have you heard about similar incident?

Best regards

Marcin