It's cold/flu season now, but online, viruses are year-round. The one rampant on Twitter since last night looks like it began on a mobile version of the social networking site, activated when folks clicked on URL's shortened using goo.gl, as you can see from this search filled with warnings not to click.
The worm appears to be taking over accounts and/or creating new ones in spreading the contaminated links. Techweet reports that those who click on the links are sent to "various malware-laden sites."
TechCrunch got on top of it early, and received this response from Twitter tech rep Troy Holden: "We’re aware and have sent out password resets for affected users. We’ll monitor the situation in case of further iterations."
To be safe, best not to click on links without any context.