The US company, listed as the worst offending ISP on a blacklist of companies that host spam services, is accused of not doing enough to prevent spam.
"MCI knows exactly what's going on," said Steve Linford, director of anti-spam organisation Spamhaus. "I've made contact with them but the situation has not improved."
MCI's lack of action resulted in an announcement from Spamhaus and a detailed description of the problem on its website.
According to Linford, Send-Safe, the program credited with creating networks of zombie computers that unwittingly send spam, is the reason for the vast majority of spam. Linford believes MCI should stop hosting websites selling Send-Safe in order to protect their customers from spam.
"MCI's executives know send-safe.com uses the MCI network to sell and distribute the illegal Send Safe proxy hijacking bulk mailer, yet MCI has been providing service to send-safe.com for more than a year," Linford said.
In a response to the Washington Post Timothy Vogel, head of MCI's technological legal team argued MCI would take action against Send-Safe if it had evidence that Send-Safe was used for spamming and not just advertising, as it claims.
Linford responded angrily on the Spamhaus website.
"This is seriously incorrect, MTI and Send-Safe are not advertising it, they're selling and distributing it. As in "Talking about heroin is a lot different than selling heroin". While commercial speech is given qualified protection under the first amendment, advertising the sale of software designed for the prime purpose of allowing the end-user to engage in illegal activities is not protected under the first amendment," he said.
Last week SC reported that new techniques will herald a rise in spam over the next six months. Malware much like the Sobig virus, written with the sole purpose of creating zombie networks, is being used to route email via ISPs and bypass spam filters.