In the last few years we must have been asked by many dozens of clients to clean up  large numbers of computers with some form of unwanted software on them – call it a virus, a worm, a trojan horse, rootkits, adware, malware, spyware, whatever – I’m just going to call it all ‘unwanted software’.

Mostly this can be cleared up with careful use of the right tools and a tried and tested methodology which we’ve built up over a considerable time.

But when it comes to handing back a freshly cleaned computer we are frequently asked the one question we find very difficult to answer,  and that is,  “ Where did the ‘unwanted software’ come from?”  “How did I get this ‘virus’?”. Usually, by the time we get the computer it is infected by multiple problems and it’s far too late to know exactly what was the original problem and where it might have come from.

However, there are a few common sources.

While it is certainly possible to pick up malicious software from someone else’s computer on your  home or work network or from an infected flash memory stick or portable hard drive – even someone else’s homemade CD or DVD, – this is actually quite rare. Most unwanted software comes to you over your Internet connection.  It either comes in with an email or via your web browser. And the sad fact is, most victims download and install it themselves without realising what they’re doing.

It is imperative that you run good up-to-date antivirus software. (Most of the worst computers we’ve had to deal with have allowed their antivirus software licence to expire.) It is also essential to keep your software up-to-date with all security patches and updates. They may be a nuisance but they come out for a reason.

Email attachments you weren’t expecting, especially from people you don’t know, should never be opened. Similarly, if an email looks even slightly suspicious, never click on any embedded links. Remember the text may say one thing but the underlying link may be something else entirely.

Then we come to the most common source of unwanted software today – the web itself.  Web pages are, of course, full of links to other webpages and resources – that’s how it works. But some of these links will cause you problems.  To a large extent it depends whose website it is.  You could be forgiven for believing that large, high profile websites like those of the BBC or large well known public companies should be safe and, on the whole, they will be, but even the best have been known to be compromised, particularly if they display advertising. Clicking on the advert may end up leading you to that dodgy download.

And downloading free gifts, games, music, videos and ‘supposedly useful’ software is the single most dangerous thing you can do.  Always read the small print. Check what other pieces of software are being bundled with your item. Avoid downloading any toolbars, search bars , and other browser add-ons.

By far the most common unwanted software we’ve come across is the ‘fake security alert’ scam. There are probably hundreds or different versions of this software around under different product names and some of it can be quite difficult to get rid off. All versions attempt to convince you that your computer has multiple security issues and that you will need to register and pay for the full version in order to clean up the mess. This is a complete scam. Never be conned into parting with any money.  They will not fix the problem, but you’ll certainly never see the money again.

Once you have this software on your computer, you may find your anti-virus software has already been compromised and system restore and other Windows tools may have been disabled. The only sensible thing to do at this point is disconnect your computer from your network and seek trusted help.

If you don’t know at this stage where your unwanted software came from, we probably won’t be able to tell you either.  But we can probably clean it up for you.