Dial-up connection window launches automatically while working

While working in the system, you might see the dial-up connection dialog coming up automatically. This is caused by some application which is trying to connect to the internet. The exact application is unknown. Most applications are configured/designed to check for updates automatically by contacting home. Some applications notify the user before contacting their servers, most don't. This may be caused by parasites as well. Adware contact their servers to fetch Ads and some Trojan may even send out your valuable information.

To prevent this automatic dialup box, turn off the Remote Access Auto Connection Manager Service. This Service creates a connection to a remote network whenever a program references a remote DNS or NetBIOS name or address. To disable this service, try these steps:

You may identify the outgoing traffic using an application-based firewall like Sygate or Zone Alarm. Also, it's advisable to scan for parasites.

There are other methods to disable Autodial as discussed in the following Microsoft Knowledge articles:

Modem Automatically Attempts to Establish a Dial-Up Connection When You Start Your Computer or Start a Program

Internet Provider Sign-in Screen Appears with Winsock Program