This was discussed in another thread, and it just occurred to me I should post a news item with more explicit instructions.<br />
The issue is that the BOINC client comes bundled with SSL certificates and these expired earlier today. Here are the basic steps to fix the problem. (Note: this works on linux and I see no reason why it shouldn't work on Windows too.)<br />
1. Download the new "ca-bundle.crt" file from here:<br />
<a href="https://1drv.ms/u/s!AsVDg7OAm7-whqEqBXKHuOie0UoBKA?e=VHwBAP" rel="nofollow">https://1drv.ms/u/s!AsVDg7OAm7-whqEqBXKHuOie0UoBKA?e=VHwBAP</a><br />
2. Replace the old ca-bundle.crt file with the new one (it should be in your BOINC root directory).