How to un-schedule Update Maneger?

[spider]

I have Ubuntu 10.04 LTS (Lucid Lynx) installed on my desktop.

Very often just after the startup, the Update Manager is launched automatically and it is annoyed because I want it to appear only when I launch it manually.

Could anybody advise me what should I do to remove the Update Manager from the launching schedule?

P.S. I have looked into man pages on cron, crontab, anacron and anacrontab but have not found any specific line in system-wide crontab or anacrontab files that should be removed.
       Moreover, the system reports that crontab files does not exist for root and the user.

Thank you.