Software maker Opera's decision to support BitTorrent has added to some security experts' worries that applications which require open connections through firewalls are becoming increasingly popular.

Last week, the Norwegian company revealed that its latest technical preview adds support for downloading BitTorrent files, or torrents. BitTorrent, a peer-to-peer protocol that speeds files sharing by allowing every client to serve up pieces of a large file, requires that firewalls allow connections to the client software.

With the adoption, the alternative Internet browser is the latest application to ask users to open ports, the numerical addresses that software applications use for communication. Some voice-over-Internet applications also require a direct connection to the Internet and need ports to be open if the hardware is placed behind a firewall.

If such applications grow more popular, security may suffer, said Johannes Ullrich, chief research officer for the Internet Storm Center, a network-threat monitoring service hosted by the SANS Institute.

"Opening more ports is never a good idea," he said. "Adding more functionality to heavily attacked applications like Web browsers isn't that great (of an idea) either."

The link for this article located at SecurityFocus is no longer available.