I encounter very bad problem on my forum I have a health and medical forum with 40k daily visitors. some times when I click one of my links instead of my content it is redirected to a long and weird url and shows a message that asks me if I want to cancel the url I do it but it is redirected to a porno website !? if I close the url and click my url I see my content without any problem.but again after 12 hours I encounter the problem . why ? what I must do ?
At first I doubted security problem on my pc like you but after I received a message from google webmaster that googlebot can`t access my site I am sure my site has problem.96% of my traffic is on my forum
Is your vBulletin up to date and do you use plugins? When yes, are they up to date too? Did you look up if the redirection is caused by mod_rewrite rules in your .htaccess file?