If you receive an e-mail supposedly from UPS regarding a parcel they are unable to deliver with an invoice attachment, or a customs form with an attachment, DELETE it immediately. I had received one on my work e-mail yesterday and coincidentally we were expecting a parcel from France, so I opened it. It wasn't until I switched on my PC this morning that I realised it had loaded a particularly nasty malware virus. You get messages saying that your PC is infected with virus's and tries to get you to go to a bogus website called Antivirus XP 2008, and then wants you to buy the removal tool using your credit card.

This wasn't initially picked up by our Macafee Antivirus software and
it took 2 of our IT guys 3.5 hours to get rid of the bloody thing, so a completely wasted morning.

They eventually got rid of it using a software called Malwarebytes' Anti-Malware. Even then they still had to re-install some files from XP installation disc that had been corrupted.
This is a real BUGGER so please beware.