Nobody but you guy's ( scff249n & m0le) are talking about flipp'in e-mails !!
My point (which scff also took up) is that these filters are not accurate even at the basic level of personal email. They can easily be dodged around by spammers.
I was trying to make the point that if personal emails can't properly be filtered from spammers and protected from malware links then anything more expansive such as a large social website would have absolutely no chance.
Yes, you can have filters that block out specific words, for instance this site, but if the spammer changes one character to something that reads as that letter but isn't that letter - try "a" for "@" then the filter is useless. Why do you think you get adverts for "V1@gr@"?
What would you put in a filter to kill the link? If you filter words that malware programmers love to use like "antivirus" found in a URL then they will just change the URL to something else. If you add that to the filter then they change it again. Filters are programmed by humans and cannot think.
Then there's the human angle. BC has a handful of mods and many great members that keep a check on the site. But YouTube and Facebook are so much larger than a forum. The videos, apps, on-screen and text comments would be impossible to screen for.
Also, you say that these large sites would rather you got a virus than they pay for monitoring? How good is it for a large company - relying on hits to drive traffic for advertisers to pay their hosting fees to run a profit - to be unwittingly passing on malware links and infections? It is an online business killer and if Google could remove it completely they would. It is their entire business.
They can't because as yet no-one can come up with a good enough filter system.