Syria's presence on the Internet suddenly went dark for around 40 minutes on 19 July, Net analysis firm Renesys has reported.

Exactly what happened between 13.32UTC and 14.42UTC on Thursday is as unclear as almost everything else that occurs in a country in a state of near civil war but the brief disconnection was highly unusual from national domains that have recently been stable.

What Renesys means by disconnection is that networks routed through Syrian Telecommunications Establishment were "withdrawn" from the global routing table, leaving only five of sixty-one Syrian prefixes available.

The five that remained turned out to be controlled by Indian company Tata which has a presence in the region meaning that all Syrian-directed domains were unavailable.

There has only been one previous outage on this scale but that lasted only minutes in October 2011, Renesys said, with a second in June 2011 disrupting only parts of the Syrian system since then.

The most likely cause of the disappearance is likely to have been Syrian Government action.

"Interestingly enough, among the websites hosted in these networks is one providing a fake Skype encryption tool, purportedly targeting Syrian opposition activists," noted Renesys.

Among a number of under-pressure Governments in the region, Syria has tended to allow Internet connectivity to continue despite it being used as a conduit for negative video footage.

Such images benefit dissidents but keeping the Internet also benefits the regime which has launched waves of malware attacks on the opposition forces using the Trojans mentioned by Renesys.