Spyware is to blame for half of all PC crashes and is putting a strain on support helplines, according to industry analysts.

It is estimated that 90 per cent of all PCs are harbouring 30 or more pieces of spyware.

Microsoft told a US Federal Trade Commission workshop last month that this type of malware causes more than half of Windows operating systems failures reported to the company, but that users rarely realise that spyware is the problem.

The same problem hits computer manufacturers, costing millions in support costs. Dell in the US reported that spyware issues now account for 12 per cent of calls to its technical support lines.

And SupportPlan, a UK IT call centre, reported a six per cent rise in spyware problems over the past three months.

ISPs also claim that spyware and other deceptive software is often the cause of slow connections or malfunctioning browsers.

This can lead subscribers to question the value of their broadband connection, because they believe that the network is the problem.

Tiscali told vnunet.com's sister title Computeractive that it is seeing a growing number of calls to support lines regarding spyware problems.

Pete Simpson, manager of the ThreatLab at security company Clearswift, told vnunet.com that the problem is getting worse.

"The advertising spyware is irritating, but the real worry is the more sinister malware and the extended threats such as keystroke loggers stealing identities and personal information," he said.

Some politicians in the US are now trying to ban spyware. New York Senator Michael Balboni has filed a bill in the State Senate to make the unauthorised uploading of spyware to a user's machine a crime.

But Stuart Okin, chief security officer at Microsoft UK, pointed out that one person's spyware is another's way of customising their internet experience.

"The trouble is that there is no clear definition of spyware," he told vnunet.com.

"Because Microsoft believes that the user should be in control, we have put controls in XP Service Pack 2 such as pop-up blockers and a firewall that alerts the user if an application is trying send information. This should help combat spyware."