On corporate networks in the last month, unsolicited email made up 90.4per cent of messages - a report by Symantec said. This shows a 5.1 increase on the previous month's figures.
But Symantec said the rise was nothing out of the ordinary.
The security software company says that for years spam has made up somewhere between 80 percent and 95 percent of all email on the internet.
Nearly 58 percent of spam is now coming from botnets - networks of hacked computers that can be misused by criminals to steal financial information, launch attacks or send spam.
Donbot is the worst of the spamming Botnets, generating 18.2 percent of all spam.
Social networks are also becoming an increasingly important spammer's tool. In just the past week criminals began taking over both Facebook and Twitter accounts, stealing users' passwords with different phishing attacks.
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