let me guess...
you have norton? and it just did an update?
ive seen some other ppl complaining about this and most seem to say it happened right after a norton update..
Quote: Originally Posted by dodplugins.net forums
I've found a solution, but it requires turning off "Auto-Protcect" on Norton AntiVirus. Apparently they had a software update last night and it keeps detecting Steam as a Trojan, and blocks its ability to run. So turning off Norton will allow you to play, however it leaves your comp at risk.