I'm trying to search twitter for evidence of near-realtime alerts or updates regarding security issues.
What hashtags are common or popular in the IT Security world?
#infosec and #security are the two main hashtags I'm aware of.
Depending on what you're interested in there are other less popular hashtags. For example:
There's also the option to use multiple hashtags in your search. If, for example, you are interested in Android security, you can search for "#android AND #security".