Comment - Viewpoint - Beware unfriendly spyware invasion. As it evolves from the being the marketer's pal into the PC user's enemy, keep an eye on spyware, warns Matt Piercy.(Column)

When is a virus not a virus? When it's a piece of spyware. Spyware - aka adware - was until recently a relatively benign snooper on surfing habits, targeting users with tailored advertising in pop-ups or emails.

The problem is that spyware is getting nasty. It's being written to record passwords and credit-card numbers, or hijack browsers and bookmark porn or other undesirable sites. Some spyware even features self-updating code so that freeware removal tools have no effect.

What's more, most people with spyware on their computers have unwittingly asked for it. Many web sites ask users to register or sign up to receive content, and by doing so, users agree that spyware can operate on their PCs.

It is not a small-scale problem. Recent US research showed that one in three PCs scanned had spyware hidden on their hard drives. Of 650,000 PCs scanned, more than 18 million spyware tools were found.

And spyware is not just confined to home-users. It has invaded business PCs because most firms don't have managed anti-spyware protection in place. Some spyware, such as that used by peer-to-peer networks, is bandwidth hungry, which can cause trouble on corporate networks.

It is such a big problem in the US that in spring 2004 the government unanimously approved the first-ever anti-spyware bill, which levies fines of up to $3m for those illegally collecting personal data, altering browsers, or stealing identities.

So how has spyware been allowed to get ...