He being an astronomy enthusiast [powered telescope and digicam and all that]
was on an astronomy website, when the up popped a very realistic Police notice warning that he is viewing an unsafe site and action could be taken- expect a visit.
There is a virus that generates similar reports. It's called the Metropolitan Police virus. Alternatively the website that was visited was hacked and a notice put up. In either case suggest an anti-virus and anti-malware scan as a matter of urgency.
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