Spamming
With recent improvements to e-mail spam filtering technology and their wider use, spammers have begun using YouTube as way to advertise: popular videos frequently have comments with links to irrelevant external sites, usually with some enticing statements (such as "Great video, go to
for the full version"). To counter this, YouTube has blocked comments with URLs in them since late 2006; if a user tries to post a comment with a URL, it will be discarded and will not show up. As of August 2007, this "feature" seems to have been extended to profile comments as well, although the user will receive an ambiguous "error processing your comment" message. However, posting links is still possible in bulletins, private messages, or group discussions. Also, if a user posts many comments in a short period, they may be asked to complete a CAPTCHA, which was implemented when a notorious spammer abused the lack of a flood control. However, the lack of a CAPTCHA is still present in some areas of the site. Other examples of spammers include users who use non-related-to-video threats (including "Post this message to friends or your mom will die in hours") They may also send messages to a user's inbox (essentially in the form of a plain-text spam email). Some of these spam accounts also posted pornographic videos on YouTube. A slightly newer feature of YouTube is the ability to send invites to people through email by using the "Invite Your Friends" feature. Originally, this feature was indeed a useful feature to build a bigger community using YouTube. When spammers became aware of this, they decided to give it a try and found every email address possible to send random email invites. More so, they've now been able to cheat the system even more.
“ The messages came from service@youtube.com. [...] The messages look like a legitimate YouTube invite, except they include typical spam content like stock pump-and-dump promotions and links to spam Web sites. Many of them use Microsoft's recent XBox 360 hit "Halo 3" as bait, telling the recipient they have won a free copy of the game and to go to a Web site. If they take the bait and click on "winhalo3.com," the Web site infects them with the Storm Worm, which has been hanging around since August.[35]
”
Spammers have used this route more often nowadays because they can use it to defeat spam filters, gain more readers and possibly customers. "They just do as all spammers do..."
source:Wikipedia
