A helpful worm is variant on a computer worm which delivers its payload by doing "helpful" actions instead of malicious actions. Welchia was a major example of a helpful worm - utilizing the same exploit that caused the Blaster worm. Infected computers automatically began downloading Microsoft

Microsoft

Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

 security updates for Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 without the users' consent and automatically rebooted the computers. One of these updates was, incidentally, the patch that fixed the exploit.

Even though they do not do anything "malicious", most helpful worms do not log events, and they automatically reboot

Booting

In computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...

the computer as part of the installation process without the user's consent. They also can put strain on the network as they spread and download updates.