A new, more dangerous version of the Netsky worm is making the rounds on the Internet.
The bug, which goes by the name Netsky-b or Moodown-b, is a modified version of NetSky-a that surfaced earlier this week. Initial ratings from the likes of Symantec, Network Associates and F-Secure suggest that the malware is a medium- to high-grade threat; and early reports say that the worm is spreading quickly.
Though not nearly as virulent or destructive as the recent MyDoom bug, Netsky-b has infected hundreds of systems, including computers within some major corporations such as Lucent, according to reports.
Netsky-b is a self-propagating -mail worm, which is delivered in executable attachments in incoming e-mails. Once the infected attachment is opened, the bug copies itself to the computer and re-sends itself to all email addresses found on the hard drive of the contaminated PC.
Some interesting and nefarious aspects of the worm include innocuous-looking file extensions on some infected files, such as .doc, .txt or .rtf. These phoney extensions, which may be designed to fool users and anti-virus software, appear before actual file type extensions such as .pif, .scr, .exe or sometimes .zip.
Emails containing the bug are also delivered with subject lines such as "hi," "information" and "stolen,". Email body messages are simple and include lines such as: "here is the document." Netsky-b also spoofs email addresses so that incoming messages may appear to come from someone with whom the potential victim is familia.
The worm affects only versions of Windows later than Windows 95 and it has the capacity to spread via file-sharing networks like Kazaa, Bearshare and Limewire. Once installed, the malicious software launches a fake error message which reads: "The file could not be opened!"
The worm also attempts to make some registry-key changes, including changes that are capable of deactivating the Mydoom.a and Mydoom.b bugs, if they exist on the victim's computer.
Anti-virus vendors and e-security experts are, as always, urging users not to open suspicious e-mails and recommending that users upgrade their anti-virus software as soon as possible.