Thank you Polonus!
The PluginDetect script checks versions of installed plug-ins, such as Java, Flash Player, Adobe Reader, VLC Player, etc. For detection to work properly, it must open a file for some plug-ins, this might cause the Trojan-like behaviour. I use this script to warn visitors in case some plug-in is out of date and insecure.
The attached script you pointed out seems to be writing "mailto: " information for the script author; no anti-virus detected it as malicious.
When can I expect some verdict from avast?