An IT privacy firm has listed its top 10 pieces of malicious code, warning that some are found hidden in popular applications.

The majority are bundled with free software, and the effects range from displaying adverts to logging every keystroke. One of the named programs, Perfect Keylogger, is currently being used in the Lycos Trojan.

"It is our goal to inform internet users of the ramifications of having potentially unwanted programs on their systems," said Richard Stiennon, vice president of threat research at Webroot, which conducted the research.

"It is their choice to keep or remove these programs based on the information available to them. We are making sure they have this information so they are making knowledgeable decisions."

The problem of software that diverts dial-up internet numbers to premium lines has grown to such an extent that Ofcom has called for an increase in the fines that can be charged, up to a maximum of £100,000.

TOP 10 MALICIOUS CODE:

PurityScan
This displays pop-ups onto your computer whenever you are online. It induces you to install it by claiming to find and delete pornographic images.

N-CASE (msbb.exe)
N-CASE delivers advertisements to your computer. This program is usually bundled with freeware applications.

Gator (GAIN)
This displays banner advertisements based on your web surfing habits and is bundled with the file-sharing program Kazaa.

CoolWebSearch (CWS)
This can hijack your web searches, home page, and Internet Explorer settings.

Transponder (vx2)
Transponder is an Internet Explorer browser helper object that monitors web use and data entered into online forms, then delivers targeted advertisements.

ISTbar/AUpdate
ISTbar is a toolbar for searching pornographic websites that has been reported to display pornographic pop-ups and to hijack your homepage and internet searches.

KeenValue
KeenValue is a program that collects personal information and delivers advertisements to your computer.

Internet Optimizer
Internet Optimizer hijacks error pages and redirects them to its own controlling server at www.internet-optimizer.com.

Perfect Keylogger
Perfect Keylogger is a monitoring tool that records all visited websites, keystrokes and mouse clicks.

TIBS Dialer
TIBS Dialer is a program that hijacks your modem and dials premium numbers, usually to access pornographic 'pay' sites.