A snapshot of large US companies has found that 'viral' applications such as VoIP, instant messaging, webmail and P2P applications are now endemic on many networks.

Compiled by insider security startup Reconnex from 1.1 Terabytes of data, the figures showed alarmingly high use of these applications, regardless of company security policies.

Skype, in particular, was found to be present in 22 percent of networks, one of the first times anyone has managed to put a hard figure on its use. In most cases, companies were not aware of how widespread the application had become, or had no means of tracking it.

Eighty-nine percent of companies had webmail running from within the firewall, 78 percent IM, and 78 percent P2P applications.

The statistics survey covered only a relatively small number of companies -- no more than 15 -- but these were described by Reconnex as "Fortune 1,000" and so the figures can be taken as significant.

"Skype is viewed as a potential IT nightmare," said Kevin Cheek, Reconnex's VP of product management. "They (companies) are dreading having to deal with it. It's really about what you don't know."

The beta of version 2.5, released last week, increased the problems of the application. In addition to being highly evasive in its design, a Skype client could now set up collaborative sessions with up to 100 users, he said. Most customers had no idea the application was present on their network, or how many individuals were using it.

Reconnex markets iGuard, an appliance for monitoring and analyzing (though not blocking) application activity, including that of hard-to-track software such as Skype.

The Reconnex Insider Threat Index for the first quarter of 2006, can be viewed in full on the company's website.