Computer viruses spread by e-mail are growing more sophisticated as virus writers and “spammers” are thought to be joining forces in an effort to make smarter bugs, a computer security group said on Tuesday. New York-based MessageLabs, which scans client e-mails for viruses to block, said it picked apart some 5.6 billion e-mails from January to June this year and found 1-in-12 contained some sort of virus that penetrated firewalls meant to block them. MessageLabs typically scans about 50 million customer e-mails daily, and its customers include major government and corporate entities from the British government to The Bank Of New York and Japanese technology giant Fujitsu Ltd.