[Background] Below is a draft of a department notice to be sent to the company-wide group. I think it is poorly written, but I cannot say exactly what is wrong.
[Task] Please help me revise it in three steps:
Step 1: Score the draft against the 3 criteria below, 1–5 points each, and explain the reasons for deductions;
Step 2: Rewrite it;
Step 3: Score the rewrite against the same criteria. If any item is below 4 points, revise again until every item reaches 4 points, then give me the final version.
[Scoring criteria]
1. Instantly clear what to do: time and action in the first two sentences;
2. Complete information: use only the content in "Known information" below, omit nothing, and invent nothing new;
3. Sounds like a colleague talking: no bureaucratic tone, within 150 words total.

[Known information]
Starting 7 pm on October 15 (Thursday), the IT department will install new antivirus software on everyone's computers, about 1 hour. Before leaving work, please: save your files; do not shut down your computer; plug in the power. For problems, contact Xiao Zhou in IT, extension 8021.

[Draft]
Dear colleagues: To further strengthen the company's information security management and effectively raise the security awareness of all employees, after company research and decision, a computer system upgrade will be carried out in the near future. At that time, please actively cooperate, make relevant preparations in advance, and ensure the upgrade proceeds smoothly. If you have any questions, please contact the relevant department in a timely manner. Thank you for your understanding and support!