However, since Kaseya’s software is used by large IT companies that provide contractual services to hundreds of smaller businesses, the hack could spread to thousands of victims. Kaseya warned all of its nearly 40,000 customers to immediately disconnect from their Kaseya software. Cybersecurity firm Huntress Labs said it had tracked 20 affected IT companies called managed service providers. Over 1,000 customers of these companies, mostly small businesses, were also affected by the hack. Huntress Labs said on Reddit.