What’s wrong with this sentence?
Once infected, the worm turns off Windows Update services, thereby preventing the machine from obtaining the very patch that would have prevented the initial exploit.
Answer: When you begin a sentence with an introductory phrase followed by a comma, the thing that the phrase refers to should immediately follow the comma. In this example, the writer unintentionally says that the worm gets infected. Worms don’t get infected — they cause infections.
By changing the sentence to make sure that whatever follows the comma is the thing that is being modified, the sentence meaning becomes clear.
Once the worm finds a vulnerable machine, it turns off Windows Update services and prevents the machine from obtaining the very patch that would have prevented the initial exploit.
How else could you correct today’s sentence?