Beware when receiving email from unknown people, inviting you to watch a YouTube clip. When clicked on the URL link, instead of going to YouTube site, you will be asked to download some files. These files will install few computer viruses / worms into your pc which will execute codes to attack any pcs it found out there. This means, your office pcs are not spared from the attack. These attacks will not only making your pc slow, but others too.