BOINC.exe just tried to download trojan.gen2.

Reference file was hadam3p_afr_7.22_windows_intelx86.exe

In 99.99% of the cases this is a false positive, because the anti-virus product finds that some routine in the project's science application looks suspicious.
Which is why we advise people to exclude their BOINC Data directory from being actively scanned by anti-virus and other anti-malware products and to only scan the data directory with BOINC not running.

When you tell which AV product you use, someone will be able to tell you how to exclude BOINC its data directory from being scanned by it.
If you do not trust it, you can check through https://www.virustotal.com/ if it's only you or if it's also found to be affected by their list of 50+ scanners.
Also report this on the project's forums, in this case it looks like ClimatePrediction.net.

In the 0.01% chance it is infected, it usually got infected on your system.
Both BOINC and the project's servers run Linux, not impossible to infect by outside forces, but highly unlikely.

Edit: I have written down for a lot of AV products how to exclude the data directory.

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BOINC.exe just tried to download trojan.gen2.

Reference file was hadam3p_afr_7.22_windows_intelx86.exe

This particular file has already been discussed in a Climate Prediction message board thread, although unfortunately the poster mis-judged which thread to discuss it in.

Have a look in Scheduler process down?