In its blog post on critical Exchange Server patches Tuesday, Microsoft pointed to "limited and targeted" exploitation of three vulnerabilities in the wild.

But new data suggests that the breaches may not be limited or targeted at all.

"We took a sample of about 2,000 or so of our partners' [servers]. We saw 400 that are vulnerable, an extra 100 that are potentially vulnerable and 200 and growing that were compromised," said John Hammond, a senior security researcher at Huntress, which focuses on security solutions for small and medium businesses.

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